SYNTHESIS AND CHARACTERIZATION

OF PURE AND DOPED CONDUCTING AND

SEMICONDUCTING MATERIALS

THESIS

SUBMITTED TO THE

UNIVERSITY OF LUCKNOW

FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

IN

PHYSICS

UNDER THE SUPERVISION OF

Prof. R. K. Shukla

BY

INDRA BAHADUR M.Sc. (Physics)

DEPARTMENT OF PHYSICS

UNIVERSITY OF LUCKNOW

LUCKNOW 226007 – INDIA

JANUARY-2015

CONTENTS

CERTIFICATE

Page No.

ACKNOWLEDGEMENTS i

SUMMARY iii-vi

Chapter 1 Introduction 1-50

1.1 Materials 1

1.1.1 Classification of materials 2

1.1.2 Conducting and Semiconducting materials 5

1.2 Materials used as dopant (Al2O3, CuO, TiO2) 9

1.3 Conducting Polymers (Polythiophene,

Polyaniline, Polypyrrole)

13

1.3.1 Historical developments 15

1.3.2 Doping in conducting polymers 16

1.3.3 Metal-insulator transition in doped conducting

polymers

21

1.3.4 Importance of Conducting Polymers as

Sensors

26

1.3.5 Ionization in Conducting Polymers 27

1.3.6 Bulk and nanopolymer 28

1.3.7 Applications of Polymer 29

1.4 Synthesis of Polymers and Polymer

Composites

29

1.4.1 Preparation of Thin films 30

1.4.2 Sol-gel Process 32

1.4.3 Sol-gel spin coating 34

1.4.4 Spray pyrolysis 35

1.4.5 Dip Coating film 37

1.5 Characterization Techniques 38

1.5.1 X-Ray Diffraction (XRD) 39

1.5.2 Scanning Electron Microscopy (SEM) 40

1.5.3 Fourier Transform Infrared Spectroscopy 43

(FTIR)

1.5.4 UV-visible Spectroscopy (UV-vis) 44

1.5.5 Photoluminescence Spectroscopy(PL) 45

1.6 Objective of present work 48

1.7 Organization of present work

49

Chapter 2 Synthesis and Characterization of Undoped

and Al2O3 Doped Polythiophene

Nanocomposites

51-65

2.1 Introduction 51

2.2 Experimental 53

2.2.1 Chemicals 53

2.2.2 Sample preparation 53

2.2.3 Characterizations 54

2.3 Results and discussion 54

2.3.1 Structural study 54

2.3.2 Morphological study 55

2.3.3 Optical properties 60

2.4 Conclusion

65

Chapter 3

Synthesis and Characterization of

Chemically Synthesized Undoped and CuO

Doped Polyaniline Nanocomposites

66-80

3.1 Introduction 66

3.2 Experimental 68

3.2.1 Pellet preparation 68

3.2.1 Characterizations 68

3.3 Results and discussion 69

3.3.1 X-ray Diffraction 69

3.3.2 Scanning Electron Microscopy 72

3.3.3 Optical Properties 74

3.4 Conclusion

80

Chapter 4

Synthesis and Characterization of Undoped

and Al2O3 Doped Polypyrrole

Nanocomposites

81-93

4.1 Introduction 81

4.2 Experimental 83

4.2.1 Synthesis of Polypyrrole 83

4.2.2 Characterizations 83

4.3 Results and discussion 84

4.3.1 X-Ray Diffraction (XRD) 84

4.3.2 Scanning Electron Microscopy (SEM) 85

4.3.3 Optical Properties 88

4.4 Conclusion

93

Chapter 5

Structural, Morphological and Optical

Studies of Undoped and Al2O3 Doped

Polyaniline Thin Films

94-108

5.1 Introduction 94

5.2 Experimental 96

5.2.1 Synthesis of Polyaniline 96

5.2.2 Characterizations 97

5.3 Results and discussion 98

5.3.1 X-ray diffraction (XRD) 98

5.3.2 Scanning Electron Microscopy (SEM) 100

5.3.3 Optical Properties 102

5.4 Conclusion

108

Chapter 6

Structural, Morphological and Optical

Studies of Undoped and TiO2 Doped

Polypyrrole Thin Films

109-124

6.1 Introduction 109

6.2 Experimental 112

6.2.1 Sample preparation 112

6.2,2 Characterizations 113

6.3 Results and discussion 114

6.3.1 Structural Analysis 114

6.3.2 Scanning Electron Microscopy (SEM) 115

6.3.3 Optical Properties 118

6.4 Conclusion

124

Chapter 7

Conclusion 125-130

References 131-152

Laboratory Instruments 153-161

i

ACKNOWLEDGEMENTS

“I am the only one, But still I am one.

I cannot do everything, But still I can do something.

I will not refuse to do, The something I can do.”

During the entire course of time, I was assisted by many people

and it is indeed my pleasure to express my gratitude for all of them.

At this fortuitous moment, I take this opportunity to express my

profound gratitude to my esteemed supervisor Prof. R. K. Shukla,

Department of Physics for his exemplary guidance, monitoring and

constant encouragement throughout the course of this thesis. His patience

and support rescued me from despair on countless occasions. The help,

advice, guidance and blessing given by him time to time shall carry me

long way in the journey of life.

I gratefully acknowledge the advice and guidance of Prof. Kirti

Sinha, Head, Department of Physics, Prof U. D. Misra, University of

Lucknow, without which this assignment would not have been possible.

I also take this opportunity to express enormous thanks to Prof.

Anchal Srivastava, Department of Physics for her cordial support,

providing characterizations facility, valuable information and guidance

which helped me in completing this task through various stages.

I also take this opportunity to express enormous thanks to Sri

Tarun Gauba (IPS), ADC to Governor UP, Sri Indra Jeet Singh Rawat

(C.S.O. Rajbhawan) and all my senior’s and well wishers from

Rajbhawan, Lucknow for their cordial support.

I express my sincere thanks to my colleague Dr. Akhilesh Tripathi,

Mr. Nishant Pandey, Dr. Sheo kumar Mishra, Mr. Susheel Singh and Mr.

Arvind Verma, Ms. Divyanshi and Mr. Vijendra for their cooperation and

ii

willingness to share their knowledge to understand and complete this

task.

I would like to thank the members of Departments of Physics,

University of Lucknow. Thanks to all of my friends, especially

Dharmendra Pratap Singh, Anoop, Abhishek, Dr. Puneet Pandey and Mr.

Vrijesh Pandey for their encouragement.

Last, but certainly not least, my deepest thanks go to my mother

Smt. Jadawati Devi, my wife Mrs Saroja Yadav and my children, younger

brother Mahendra Yadav and my heartiest friends Dr. R. K. Mishra, Dr.

M. L. Pal and Sri C. J. Yadav for supporting and encouraging me to

achieve this goal and be successful. I am forever grateful to them for

showing me the value of education.

Lastly, and most importantly, I am grateful to the almighty GOD

without whom this assignment would not be possible.

In the end of my acknowledgement, I would like to convey my

message to the next generation that I have learned during the Ph.D.

program, communicating by following lines of Confucius :-

“To be able under all circumstances to practice five things

constitutes perfect virtue; these five things are gravity, generosity of soul,

sincerity, earnestness and kindness.”

(Indra Bahadur)

iii

SUMMARY

Chapter 1 deals with the brief introduction of materials, their types and

applications. In this chapter, we have discussed about basics of materials

and three conducting polymers including polythiophene (PTh),

polyaniline (PAni) and polypyrrole (PPy) and their metal

nanocomposites. The metal dopants such as Al2O3, CuO and TiO2 have

been discussed in the present work. It also deals the discussion of

deposition techniques of the thin films as well as characterization

techniques. It also contains the organization and objective of thesis.

In Chapter 2 undoped and Al2O3/polythiophene nanocomposites have

been synthesized by chemical oxidation method. All the samples are

characterized by X-ray diffraction (XRD), Scanning electron microscopy

(SEM), Ultraviolet visible Spectroscopy (UV-vis), Photoluminescence

(PL) spectra and Fourier transform infra red (FTIR) spectroscopy. XRD

spectra show the polycrystalline nature of all the samples. SEM images

are indicating formation of spherical shape of nanostructures. As-

synthesized samples of undoped polythiophene and Al2O3/PTh

nanocomposites exhibit many pores on the surface of nanostructures.

Synthesis of Al2O3 polythiophene composite material is confirmed by

FTIR spectroscopy. UV-visible absorption spectra show absorption peak

at around 300 nm which is due to π- π* inter-band-transition of PTh rings.

A small change in optical absorption spectra is observed which can be

associated with the degree of oxidation. PL spectra exhibit mainly three

visible emission peaks at around 462 nm, 490 nm and 522 nm. The two

emission peaks 462 nm and 490 nm in the Soret band region whereas

single peak at 522 nm in the Q band emission. The intensity and peak

position of polythiophene have been randomly changed with amount of

Al2O3 dopant.

iv

Chapter 3 deals with synthesis of undoped and CuO/PAni

nanocomposite by the chemical oxidation method at room temperature

and their characterizations. The prepared samples have been

characterized by XRD, SEM, FTIR, UV- visible and photoluminescence

spectroscopy. XRD spectra show weak crystalline quality of all the

samples, whereas the PAni synthesized is amorphous in nature. The

scanning electron microscopy images of all the samples show granular

coral like structure. The study of FTIR spectra confirm the formation of

conducting PAni and also suggests that doping of CuO in PAni does not

affect the structures. The UV–visible absorption spectra of the solutions

of all the samples contain some peak at 305 nm. The observed

bathochromic shift at the intense absorption band 305 nm is due to the π-

π* transition of benzenoid ring. The PL spectra of 0, 2, 4, 6 and 8 wt%

CuO/PAni samples show peaks in visible emission region which at

around 362 nm, 405 nm in violet region 459 nm, 486 nm in blue region

and 528 nm in green region.

In Chapter 4, we have synthesized undoped and Al2O3 doped PPy

samples by chemical oxidation method. The prepared samples have been

characterized by XRD, SEM, FTIR, UV-Vis and PL. X-ray diffraction

patterns of PPy/Al2O3 nanocomposites result show several broad peaks

while undoped sample shows only one single peak indicating poor

crystalline phase of PPy. In the SEM images, the results were found

granular coral like structures. As a characteristic of Polypyrrole,

secondary nucleation also takes place because of which the granular coral

like particles come together to form aggregates. We noticed that as the

amount of Al2O3 was increased; the number of pores and the size of pores

were also increased, which is very important for sensing. The study of

FTIR spectra confirms the formation of PPy and also suggests that doping

v

of Al2O3 in PPy does not affect its structure. The UV absorption can

significantly determine the interaction between the Al2O3 and PPy.

Solutions of all the samples show peak, which oriented around 306 nm.

The peak at 306 nm is associated with the exciton transition of π–π*. PL

shows the main emission band of the nanocomposites, located at 365 nm

with two shoulders at 473 and 533 nm. The direct band gap energies of

the PPy/Al2O3 nanocomposite of different ratios are found as 3.09 and

2.19 eV. The band gap gets decreased due to increased content of Al2O3

nano particles.

In chapter 5, we have synthesized undoped and Al2O3 doped PAni

samples by the chemical oxidation method. The prepared samples have

been characterized by XRD, SEM, FTIR, UV-Vis and PL. The XRD

spectra shows a peak around 25o which confirm the synthesis of PAni and

another peak at 55.08o

for 8 wt% Al2O3 doped PAni which as the

confirmations of successful doping in PAni. The study of FTIR spectra

confirms the formation of PAni and also suggests that doping of Al2O3 in

PAni does not affect its structure. The SEM images of all the samples

show coral like structure. UV spectra show single broad peak at around

305 nm and small peak at around 450 nm. The peak 305 nm is associated

with the exciton transition of π-π*. The longer wavelength peak at around

450 nm can be associated to the transition between benzenoid to quinoid

rings. PL spectra recorded with excitation wavelength 325 nm show a

strong UV peak at 384 nm with weak visible peak at 484 nm and 527 nm.

In Chapter 6, we have prepared undoped PPy and TiO2 doped PPy thin

films by sol-gel spin coating method. The prepared samples have been

characterized by XRD, SEM, FTIR, UV-Vis and PL. XRD spectra show

the weak crystalline quality of all the samples. SEM images show the

sphere shape of nanostructures. The amount of TiO2 doping increases the

vi

number of pores as well as size of the pores that play a very important

role in sensing of gas. The study of FTIR spectra confirms the formation

of conducting PPy which suggests that doping of TiO2 in PPy does not

affect its structures. All the samples of PPy and PPy/TiO2 nanocomposites

thin films show the peak at 309 nm which is assigned to the π-π*

transition or the excitation transition. The PL spectra of PPy and TiO2

doped PPy show three main peaks, first is in UV region around at 368

nm, second broad peak in visible region around 480 nm and another sharp

peak at around 530 nm in green region.

Chapter 7 deals with the conclusion of all the work and the

recommendations for further work.

1

Chapter 1

Introduction

The entire work, presented here, for the doctoral degree in physics is

focused on material science. Material science is an interdisciplinary field

which deals with the discovery and design of new materials. It is also

known as material science and engineering because it involves the study

of materials through the material paradigm (synthesis, structure,

properties and performance), its intellectual origins reach back to the

emerging fields of chemistry, mineralogy and engineering during the

enlightenment. In recent years, material science has become more widely

known as a specific field of science and engineering dedicated for the

synthesis, characterization and applications of new materials.

1.1 Materials

A material is defined as a substance (most often a solid, but other

condensed phases can be included) that is intended to be used for certain

applications. Raw materials are the pristine state of materials which are

metallurgically refined for specific use or application. Materials Science

involves the study of the relationships between the synthesis, processing,

structure, properties, and performance of materials that enable an

engineering function. It incorporates elements of physics and chemistry

and is at the forefront of nanoscience and nanotechnology research.

There are several types of materials around us as they can be found in

anything from buildings to spacecrafts. Materials can generally be

divided into two classes: crystalline and non-crystalline materials. The

traditional examples of materials are metals, ceramics and polymers. New

and advanced materials that are being developed include semiconductors,

nanomaterials and biomaterials etc [1].

2

Basically the materials science involves in studying the structure of

materials and relating them to their properties including electrical, optical

and electronic properties. Once material scientists know about their

structural property correlation, they can go onto study the relative

performance of a material in a certain applications. The major

determinants of the structure of a material and thus of its properties are its

constituent chemical elements and the way in which it has been processed

into its final form. These characteristics, taken together and related

through the laws of thermodynamics and kinetics, govern a

material‟s structure and thus its properties. The formation of materials for

a specific use from its raw state is shown in Fig. 1.1.

1.1.1 Classification of Materials

Materials are classified into two classes:

(a) Crystalline materials

(b) Non-crystalline materials

Crystalline materials are the materials which contain long range order

between structural units whereas in the non-crystalline materials, the long

range order is found to be absent. A crystal or crystalline solid is

a solid material whose constituents, such as atoms, molecules or ions, are

arranged in a highly ordered microscopic structure, forming a crystal

lattice that extends in all directions. In addition, macroscopic single

crystals are usually identifiable by their geometrical shape, consisting of

flat faces with specific, characteristic orientations. Examples of large

crystals include snowflakes, diamonds and tablesalt. Most inorganic

solids are not crystals but polycrystals, i.e. many microscopic crystals

fused together into a single solid. Examples of polycrystals include most

metals, rocks, ceramics and ice.

3

Fig. 1.1: The formation of material for a specific use from its raw state.

A third category of solids is amorphous solids, where the atoms have no

periodic structure whatsoever. Examples of amorphous solids

include glass, wax and many plastics.

Polycrystalline materials are solids that are composed of

many crystallites of varying size and orientation. Crystallites are also

referred to as grains. They are small or even microscopic crystals and

form during the cooling of many materials. Their orientation can be

random with no preferred direction, called random texture, or directed,

possibly due to growth and processing conditions. Fibre texture is an

example of the latter. The areas where crystallite grains meet are known

as grain boundaries.

Most inorganic solids are polycrystalline, including all common metals,

many ceramics, rocks and ice. The extent to which a solid is crystalline

(crystallinity) has important effects on its physical properties. Sulfur,

4

while usually polycrystalline, may also occur in other allotropic forms

with completely different properties. Although crystallites are referred to

as grains, powder grains are different, as they can be composed of smaller

polycrystalline grains themselves. While the structure of a

(monocrystalline) crystal is highly ordered and its lattice is continuous

and unbroken, amorphous materials, such as glass and polymers, are non-

crystalline and do not display any structures as their constituents are not

arranged in an ordered manner. Polycrystalline structures

and polycrystalline phases are in between these two extremes.

In condensed matter physics and material science, an amorphous or non-

crystalline solid is a solid that lacks the long-range order characteristic of

a crystal. In some older books, the term has been used synonymously

with glass. Now days, amorphous solid is considered to be the over-

arching concept and glass the more special case. A glass is an amorphous

solid that exhibits a glass transition [2]. Polymers are often amorphous.

Other types of amorphous solids include gels, thin films, and

nanostructured materials. Fig. 1.2 differentiates between crystalline,

polycrystalline and amorphous materials. Some of the crystal is

composed of many small grains, if the arrangements between the grains

are no rules, this is called polycrystalline crystal, such as copper and iron.

But there are also the crystal itself is a complete large grains, the crystal

is called single crystal, crystal and crystal diamond. A metallic system

can be made amorphous by decreasing the chance of crystallization:–

Allow less time for crystallization during solidification – Rapid

solidification processing (RSP).

5

Fig.1.2: Differentiation between crystalline, polycrystalline and

amorphous materials.

Generally, materials are inorganic including metals, ceramics as well as

organic materials include polymers etc. Some advance and important

organic and inorganic materials that are synthesized in the present time in

form of bulk, nanomaterials and biomaterials, etc for new industrial

applications.

1.1.2 Conducting and semiconducting materials

Conductor is an object or type of material that allows the flow

of electrical current in one or more directions. For example, a wire is an

electrical conductor that can carry electricity along its length. In metals

such as copper or aluminium, the movable charge particles are electrons.

Positive charges may also be mobile, such as the cationic electrolyte(s) of

a battery, or the mobile protons of the proton conductor of a fuel

cell. Insulators are non-conducting materials such as diamonds, glass, etc.

Copper has a high conductivity. Annealed copper is the international

6

standard to which all other electrical conductors are compared. The main

grade of copper used for electrical applications, such as building

wire, motor windings, cables and busbars. Silver is more conductive than

copper, but due to cost it is not practical in most cases. However, it is

used in specialized equipment, such as satellites, and as a thin plating to

mitigate skin effect losses at high frequencies.

Aluminium wire, which has 61% of the conductivity of copper, has been

used in building wiring for its lower cost. By weight, aluminum has

higher conductivity than copper, but it has properties that cause problems

when used for building wiring. It can form a resistive oxide within

connections that makes wiring terminals heat. Aluminum can "creep,"

slowly deforming under load, eventually causing device connections to

loosen, and also has a different coefficient of thermal

expansion compared to materials used for connections. This accelerates

the loosening of connections. These effects can be avoided by using

wiring devices approved for use with aluminium. Aluminium wires used

for low voltage distribution, such as buried cables and service drops,

require use of compatible connectors and installation methods to prevent

heating at joints. Aluminum is also the most common metal used in high-

voltage transmission lines, in combination with steel as structural

reinforcement. Anodized aluminum surfaces are not conductive. This

affects the design of electrical enclosures that require the enclosure to be

electrically connected.

Organic compounds such as octane, which has 8 carbon atoms and 18

hydrogen atoms, cannot conduct electricity. Oils are hydrocarbons, since

carbon has the property of tetracovalency and forms covalent bonds with

other elements such as hydrogen, since it does not lose or gain electrons,

thus does not form ions. Covalent bonds are simply the sharing of

7

electrons. Hence, there is no separation of ions when electricity is passed

through it. So the liquid (oil or any organic compound) cannot conduct

electricity. While pure water is not an electrical conductor, even a small

portion of impurities, such as salt, can rapidly transform it into a

conductor.

A semiconductor material has an electrical conductivity value between

a conductor such as copper and an insulator such as glass.

Semiconductors are the foundation of modern electronics. The modern

understanding of the properties of a semiconductor relies on quantum

physics to explain the movement of electrons and holes in a crystal

lattice. An increased knowledge of semiconductor materials and

fabrication processes has made possible continuing increases in the

complexity and speed of microprocessors and memory devices.

The electrical conductivity of a semiconductor material increases with

increasing temperature, which behaviour is opposite to that of a

metal. Semiconductor devices can display a range of useful properties

such as passing current more easily in one direction than the other,

showing variable resistance, and sensitivity to light or heat. Because the

electrical properties of a semiconductor material can be modified by

controlled addition of impurities or by the application of electrical fields

or light, devices made from semiconductors can be used for

amplification, switching, and energy conversion [3]. Current conduction

in a semiconductor occurs through the movement of free electrons and

holes, collectively known as charge carriers. Adding impurity atoms to a

semiconducting material, known as doping, greatly increases the number

of charge carriers within it. When a doped semiconductor contains mostly

free holes it is called p-type, and when it contains mostly free electrons it

is known as n-type. The semiconductor materials used in electronic

8

devices are doped under precise conditions to control the location and

concentration of p-type and n-type dopants. A single semiconductor

crystal can have many p-type and n-type regions; the p–n

junctions between these regions are responsible for the useful electronic

behaviour. Some of the properties of semiconductor materials were

observed throughout the mid 19th

and first decades of the 20th century.

Development of quantum physics in turn allowed the development of

the transistor in 1948. Although some pure elements and many

compounds display semiconductor properties, silicon, germanium, and

compounds of gallium are the most widely used in electronic devices.

Semiconductors are defined by their unique electric conductive behavior,

somewhere between that of a metal and an insulator. The differences

between these materials can be understood in terms of the quantum

states for electrons, each of which may contain zero or one electron (by

the Pauli Exclusion Principle). These states are associated with

the electronic band structure of the material. Electrical conductivity arises

due to the presence of electrons in states that are delocalized (extending

through the material), however in order to transport electrons a state must

be partially filled, containing an electron only part of the time [4]. If the

state is always occupied with an electron, then it is inert, blocking the

passage of other electrons via that state. The energies of these quantum

states are critical, since a state is partially filled only if its energy is near

the Fermi level.

High conductivity in a material comes from it having many partially

filled states and much state delocalization. Metals are good electrical

conductors and have many partially filled states with energies near their

Fermi level. Insulators, by contrast, have few partially filled states, their

Fermi levels sit within band gaps with few energy states to occupy.

9

Importantly, an insulator can be made to conduct by increasing its

temperature: heating provides energy to promote some electrons across

the band gap, inducing partially filled states in both the band of states

beneath the band gap (valence band) and the band of states above the

band gap (conduction band). An intrinsic semiconductor has a band gap

that is smaller than that of an insulator and at room temperature

significant numbers of electrons can be excited to cross the band gap.

A pure semiconductor, however, is not very useful, as it is neither a very

good insulator nor a very good conductor. However, one important

feature of semiconductors (and some insulators, known as semi-

insulators) is that their conductivity can be increased and controlled

by doping with impurities and gating with electric fields. Doping and

gating move either the conduction or valence band much closer to the

Fermi level, and greatly increase the number of partially filled states.

Some wider-band gap semiconductor materials are sometimes referred to

as semi-insulators. When undoped, these have electrical conductivity

nearer to that of electrical insulators; however they can be doped (making

them as useful as semiconductors). Semi-insulators find suitable

applications in micro-electronics. An example of a common semi-

insulator is gallium arsenide [5]. Some materials, such as titanium

dioxide, can even be used as insulating materials for some applications,

while being treated as wide band-gap semiconductors for other

applications.

1.2 Materials used as dopant:

In the present work several oxide materials has been incorporated in the

host materials such as Al2O3, CuO and TiO2. Aluminium oxide is

a chemical compound of aluminium and oxygen with the chemical

formula Al2O3. It has a wide band-gap of ~8.8 eV for bulk material.

10

Al2O3 has been extensively investigated dopants to serve as catalysts, fire

redundant, absorbents and fillers for structural materials [6]. It is stable in

acidic and oxidative mediums and well known for reactivity with

aromatic organic materials.

It is the most commonly occurring of several aluminium oxides, and

specifically identified as aluminium (III) oxide. It is commonly

called alumina, and may also be called aloxide or alundum depending on

particular forms or applications. It commonly occurs in its crystalline

polymorphic phase α-Al2O3, in which it comprises the mineral corundum,

varieties of which form the precious gemstones ruby and sapphire.

Al2O3 is significant in its use to produce aluminium metal, as

an abrasive owing to its hardness, and as a refractory material owing to its

high melting point.

Al2O3 is an electrical insulator but has a relatively

high thermal conductivity around 30 Wm−1

K−1

[6] for a ceramic material.

Aluminium oxide is insoluble in water. It is usually found in crystalline

form, called corundum or α-aluminium oxide, its hardness makes it

suitable for use as an abrasive and as a component in cutting tools.

Aluminium oxide is responsible for the resistance of metallic aluminium

to weathering. Metallic aluminium is very reactive with atmospheric

oxygen, and a thin passivation layer of aluminium oxide (4 nm thickness)

forms on any exposed aluminium surface [6]. This layer protects the

metal from further oxidation. The thickness and properties of this oxide

layer can be enhanced using a process called anodising. A number

of alloys, such as aluminium bronzes, exploit this property by including a

proportion of aluminium in the alloy to enhance corrosion resistance. The

aluminium oxide generated by anodising is typically amorphous, but

discharge assisted oxidation processes such as plasma electrolytic

11

oxidation result in a significant proportion of crystalline aluminium oxide

in the coating, enhancing its hardness.

Copper (II) oxide or cupric oxide (CuO) is the higher oxide of copper. As

a mineral, it is known as tenorite. It is a black solid with an ionic structure

which melts above 1200 °C with some loss of oxygen. It can be formed

by heating copper in air:

2 Cu + O2 → 2 CuO

Copper (II) oxide belongs to the monoclinic crystal system, with

a crystallographic point group of 2/m or C2h. The space group of its unit

cell is C2/c, and its lattice parameters are a = 4.6837, b = 3.4226, c =

5.1288, α = 90°, β = 99.54 °, γ = 90°. The copper atom is coordinated by

four oxygen atoms in an approximately square planar configuration [7].

Cupric oxide is used as a pigment in ceramics to produce blue, red, and

green (sometimes gray, pink, or black) glazes. It is also used to

produce cuprammonium hydroxide solutions, used to make rayon. It is

also occasionally used as a dietary supplement in animals, against copper

deficiency. Copper (II) oxide has application as a p-type semiconductor,

because it has a narrow band gap of 1.2-1.8 eV. It is an abrasive used to

polish optical equipment. Cupric oxide can be used to produce dry cell

batteries. It has been used in wet cell batteries as the cathode, with

lithium as an anode, and dioxalane mixed with lithium perchlorate as the

electrolyte. Copper (II) oxide can be used to produce other copper salts. It

is used in welding with copper alloys.

Titanium dioxide is known as titanium (IV) oxide or titania. It is the

naturally occurring oxide of titanium and its chemical formula is TiO2. It

has a wide bandgap of ~3.2 eV for bulk material. Generally it is sourced

from ilmenite, rutile and anatase. It has a wide range of applications, from

12

paint to sunscreen to food colouring. When used as a food colouring. The

most important application areas are paints and varnishes as well as paper

and plastics, which account for about 80% of the world's titanium dioxide

consumption. Other pigment applications such as printing inks, fibers,

rubber, cosmetic products and foodstuffs account for another 8%. The

rest is used in other applications, for instance the production of technical

pure titanium, glass and glass ceramics, electrical ceramics, catalysts,

electric conductors and chemical intermediates. It is in most red-coloured

candy.

Titanium dioxide is the most widely used as white pigment because of its

brightness and very high refractive index, in which it is surpassed only by

a few other materials. Approximately 4.6 million tons of pigmentary,

TiO2 are used annually worldwide and this number is expected to

increase as utilization continues to rise. When deposited as a thin films,

its refractive index and colour make it an excellent reflective optical

coating for dielectric mirrors and some gemstones like mystic fire topaz.

In paint application, it is often referred to off handedly as the perfect

white, the whitest white or other similar terms. Opacity is improved by

optimal sizing of the titanium dioxide particles. Some grades of titanium

based pigments as used in sparkly paints, plastics, finishes

and pearlescent cosmetics are man-made pigments whose particles have

two or more layers of various oxides–often titanium dioxide, iron

oxide or alumina in order to have glittering, iridescent and or pearlescent

effects similar to crushed mica or guanine-based products. In addition to

these effects a limited colour change is possible in certain formulations

depending on how and at which angle the finished product is illuminated

and the thickness of the oxide layer in the pigment particle; one or more

colours appear by reflection while the other tones appear due to

13

interference of the transparent titanium dioxide layers [8].

In some

products, the layer of titanium dioxide is grown in conjunction with iron

oxide by calcination of titanium salts (sulphates, chlorates) around 800 °C

[8] or other industrial deposition methods such as chemical vapour

deposition on substrates such as mica platelets or even silicon dioxide

crystal platelets of no more than 50 µm in diameter. The iridescent effect

in these titanium oxide particles (which are only partly natural) is unlike

the opaque effect obtained with usual ground titanium oxide pigment

obtained by mining, in which case only a certain diameter of the particle

is considered and the effect is only due to scattering. In ceramic

glazes titanium dioxide acts as an opacifier and seeds crystal formation.

Titanium dioxide has been shown statistically to increase skimmed milk's

whiteness, increasing skimmed milk's sensory acceptance score [9].

Titanium dioxide is used to mark the white lines of some tennis courts.

In the present work, various conducting and semiconducting materials

such as Al2O3, CuO and TiO2 have been used as dopant in the host

conducting polymers such as polythiophene (PTh), polyaniline (PAni)

and polypyrrole (PPy) for the synthesis of conducting polymer

composites.

1.3 Conducting Polymer

The word “polymer” is derived from ancient Greek word (poly means

"many" and mer means "parts"). Polymers are large molecules, or

macromolecules, composed of many repeated subunits. Because of their

broad range of properties, both synthetic and natural polymers play an

essential and ubiquitous role in everyday life. Polymers range from

familiar synthetic plastics such as polystyrene to natural biopolymers

such as DNA and proteins that are fundamental to biological structure

14

and function. Polymers, both natural and synthetic, are created via

polymerization of many small molecules, known as monomers. Their

consequently large molecular mass relative to small molecule compounds

produces unique physical properties, including toughness, visco-

elasticity, and a tendency to form glasses and semi-crystalline structures

rather than crystals.

Materials are generally classified into three types as insulators,

semiconductors and conductors based on their electrical properties. A

material with conductivity less than 10-7

S/cm is regarded as an insulator.

Metals have conductivity larger than 103 S/cm whereas the conductivity

of a semiconductor varies from 10-4

to 10 S/cm depending upon the

degree of doping. It is generally believed that plastics (polymers) and

electronic conductivity are mutually exclusive and the inability of

polymers to carry electricity notable them from metals and

semiconductors. Polymers are traditionally used as inert, insulating and

structural materials in many applications such as packaging, electrical

insulations and textiles.

Intrinsically conducting polymers (CPs) are different from other

conducting polymers in which a conducting material including

metal/carbon powder is dispersed in a non-conductive polymer [10].

These polymers are referred as conjugated polymers belong to a totally

different class of polymeric materials with alternate single-double or

single-triple bonds in their main chain and are capable of conducting

electricity when it is doped. Intrinsically CPs, similar to other organic

polymers, usually described by sigma (σ) and pi (π) bonds. While the σ

electrons are fixed and immobile due to the formation of covalent bonds

between the carbon atoms, the remaining π -electrons which can be easily

delocalized upon doping. Fig. 1.3 shows the molecular structures of

popular intrinsic conducting polymers such as polythiophene (PTh),

15

polypyrrole (PPy) and polyaniline (PAni) that have been used as a host

material in the present thesis work.

Polyaniline (PAni)

Fig. 1.3: Molecular structures of conjugated polymers such as

polythiophene (PTh), polypyrrole (PPy) and polyaniline (PAni).

1.3.1 Historical developments

Although polymeric materials have been used by mankind since

prehistoric times in the form of wood, bone, skin, and fibers, the

existence of macromolecules was accepted only after Hermann

Staudinger developed the concept of macro-molecules during the 1920s,

which got him the Nobel Prize in Chemistry in 1953 „„for his discoveries

in the field of macro-molecular chemistry‟‟ [11]. The research field of

conjugated (conducting) polymers came into spotlight with the

preparation of polyacetylene by Shirakawa and coworkers along with the

subsequent discovery of enhancement in its conductivity after doping

[12-15]. Some of the most important representatives in the family of

conjugated polymers in non-conducting as well as conducting forms viz.,

16

polythiophene (PTh), polyaniline (PAni) and polypyrrole (PPy) were

already being prepared chemically or electrochemically in the nineteenth

century. The existence of Polyaniline (PAni) in four oxidation states was

also recognized. A reaction scheme for the electro-oxidation of aniline at

a carbon electrode was suggested by Yasui in 1935 [16]. It was almost a

century after Letheby‟s observations that Mohilner and coworkers

reinvestigated the mechanism of the electro-oxidation of aniline in

aqueous sulphuric acid solution at a platinum electrode and characterized

polyaniline (PAni) [17]. The first real breakthrough came in 1967, when

Buvet and his group established that polyanilines are redox active

electronic conductors and PAni pellets can be used as electrodes for

conductivity measurements [18-19].

Polypyrrole (PPy), on the other hand, was known as pyrrole black and

was formed due to the oxidation of pyrrole in air. PPy is an inherently

conducting polymer with interesting electrical properties first discovered

and reported in the early 1960s [20]. It was followed by the preparation of

coherent and free standing polypyrrole films by electrochemical

polymerization by Diaz and his co-workers [21].

1.3.2 Doping in conducting polymers

Doping in conjugated organic polymers is responsible for the great

scientific and technological importance achieved by these materials since

their discovery in 1977. The concept of doping is the unique and main

issue that unites all the conducting polymers and differentiates them from

all other types of polymers [13, 14]. During the doping process, an

organic polymer such as an insulating or semi-conducting polymer could

be converted into electronic polymers exhibiting metallic conductivity

(1–105 S/cm). The concept of doping in conducting polymers is much

17

different than that in case of inorganic semiconductors. Fig. 1.4 shows a

schematic illustration to explicit the difference between the doping

mechanisms in inorganic semiconductors and conjugated polymers. In

semiconductor physics, doping describes a process where dopant content

present in small quantities occupy positions within the lattice of the host

material, resulting in a large-scale change in the conductivity of the doped

material compared to the undoped one.

The doping process in conjugated polymers is, however, essentially a

charge transfer reaction, resulting in the partial oxidation (or less

frequently reduction) of the polymer. Unlike inorganic semi-conductors,

doping in conjugated polymers is reversible in a way that upon de-doping

the original polymer can be retained with almost no degradation of the

polymer backbone. Another very important difference between the

doping in conjugated polymers and that in inorganic semiconductors is

that doping in conjugated polymers is interstitial whereas in inorganic

semiconductors the doping is substitutional.

One can easily obtain a conductivity anywhere between that of the

undoped (insulating or semiconducting) and that of the fully doped

(highly conducting) form of the polymer by simply adjusting the doping

level. During doping and de-doping processes a stabilized doped state of

the conducting polymer may be obtained using dopant counter ions by

chemical or electrochemical processes [22]. Conducting polymers can be

p or n doped chemically and electrochemically to obtain a metallic state

[13, 14]. Doping of conjugated polymers can also be carried out by

methods that introduce no dopant ions such as field induced charging

[23]. In the doped state, the backbone of a conducting polymer consists of

highly delocalized π-electrons. Fig. 1.5 represents a chart showing the

different methods that have been used usually for doping in conducting

polymers.

18

Fig. 1.4: Schematic illustration indicating the difference between the

doping mechanisms in inorganic semiconductors and conjugated

polymers.

19

Fig 1.5: Different methods for doping in conducting polymers.

Doping of conjugated polymers either by oxidation or by reduction in

which the number of electrons in the polymeric backbone gets changed is

generally referred to as redox doping [22]. The charge neutrality of the

conducting polymer is maintained by the incorporation of the counter

ions.

Redox doping can be further subdivided into three main classes: p type

doping, n type doping and doping involving no dopant ions viz., photo-

doping and charge injection doping [24, 25]. Both chemical and

20

electrochemical redox doping techniques can be employed to dope

conjugated polymers either by removal of electrons from the polymer

back-bone chain (p-doping) or by the addition of electrons (n-doping) to

the chain. In chemical doping the polymer is exposed to an oxidizing

agent such as iodine vapours or a reducing agents viz., alkali metal

vapours, whereas in electrochemical doping process a polymer coated,

working electrode is suspended in an electrolyte solution in which the

polymer is insoluble, along with separate counter and reference

electrodes.

Photo-doping is a process where conducting polymers can be doped

without the insertion of cations or anions simply by irradiating the

polymer with photons of energy higher than the band gap of the

conducting polymer. This leads to the promotion of electrons to higher

energy levels in the band gap. Charge injection doping is another type of

redox doping that can also be used to doped an undoped conducting

polymer [23, 26, 27]. In this method, thin film of conducting polymer is

deposited over a metallic sheet separated by a high dielectric strength

insulator.

The non-redox doping of conducting polymer is a process of doping

conducting polymers in which the number of electrons associated with

the polymer chain is kept constant. In fact it is the energy level in the

conducting polymer that gets rearranged in the non-redox doping process

[28]. The best example of non-redox doping is the conversion of

emeraldine base form of polyaniline to protonated emeraldine base

(polysemiquinone radical cation) when treated with protic acids [19]. It

has been observed that the conductivity of polyaniline is increased by

approximately 10 orders of magnitude by non-redox doping. Ion

implantation and heat treatment methods have also been used to dope

21

conducting polymers, however, it has rarely been used for doping

conducting polymers.

1.3.3 Metal-Insulator transition in doped conducting

polymers

Metal-Insulator (M-I) transition is one of the most interesting physical

aspects of conducting polymers. When the mean free path becomes less

than the inter-atomic spacing due to increase in disorder in a metallic

system, coherent metallic transport is not possible [29]. When the

disorder is sufficiently large, the metal exhibits a transition from the

metallic to insulating behaviour. As a result of this transition which is

also known as the Anderson transition all the states in a conductor

become localized and it converts into a Fermi glass [30] with a

continuous density of localized states occupied according to Fermi

statistics. Although there is no energy gap in a Fermi glass but due to the

spatially localized energy states a Fermi glass behaves as an insulator

[30]. It has been found that electrical conductivity of a material near the

critical regime of Anderson transition obeys power law temperature

dependence [31]. This type of M-I transition has been observed for

different conducting polymers viz., polyacetyle, polyaniline, polypyrrole

and poly(p-phenylene vinylene) etc. and is particularly interesting

because the critical behaviour has been observed over a relatively wide

temperature range [32]. In conducting polymers, the critical regime is

easily tunable by varying the extent of disorder by means of doping or by

applying external pressure and/or magnetic fields [32]. In the metallic

regime, the zero temperature conductivity remains finite, and σ(T) remains

constant as T approaches zero [32]. Although disorder is generally

recognized to play an important role in the physics of metallic polymers,

22

the effective length scale of the disorder and the nature of the M-I

transition [33-34].

In the present thesis, we have taken three most popular host conducting

polymers such as polythiophene (PTh), polyaniline (PAni) and

polypyrrole (PPy) for the synthesis of conducting polymer composites.

Polythiophene (PTh) is one of the most valuable types of conducting

polymers that may be easily modified to afford a variety of useful

electrical and physical properties such as solubility, electrical

conductivity, mobility and others. Polythiophenes are the polymerization

of thiophene (a sulphur heterocycle), i.e. a linear chain of thiophene

monomers. It possesses lower band gap and better electronic properties. It

may give rise some very useful properties such as increased ionization

potential and stability. Polythiophenes usually do not possess metallic

type conductivity even in a doped state. Therefore, they are much more

commonly used as organic semiconductors. Many of them possess also

good luminescent, nonlinear-optical, and other useful optoelectronic

properties [14]. It is polymerized thiophene of a sulfur heterocycle. They

can become conducting when electrons are added or removed from

the conjugated π-orbitals via doping. The study of polythiophenes has

intensified over the last three decades. The maturation of the field of

conducting polymers was confirmed by the awarding of the 2000 Nobel

Prize in Chemistry to Alan J. Heeger, Alan Mac Diarmid, and Hideki

Shirakawa for the discovery and development of conductive polymers.

The most notable property of these materials, electrical conductivity,

results from the delocalization of electrons along the polymer backbone

hence the term synthetic metals. However, conductivity is not the only

interesting property resulting from electron delocalization. The optical

properties of these materials respond to environmental stimuli, with

23

dramatic colour shifts in response to changes in temperature, applied

potential, solvent and binding to other molecules. Both colour changes

and conductivity changes are induced by the same mechanism. The

twisting of the polymer backbone and disrupting conjugation makes

conjugated polymers attractive as sensors that can provide a range of

optical and electronic responses.

Polythiophene (PTh)

Polypyrrole (PPy) is a type of organic polymer formed by polymerization

of pyrrole. It is also known as conducting polymers. The Nobel Prize in

Chemistry was awarded in 2000 for work on conductive polymers

including polypyrrole [15].

24

Most commonly PPy is prepared by oxidation of pyrrole, which can be

achieved using ferric chloride in methanol:

n C4H4NH + 2 FeCl3 → (C4H2NH)n + 2 FeCl2 + 2 HCl

Polymerization is thought to occur via the formation of the pi-radical

cation C4H4NH+. This electrophile attacks the C-2 carbon of an un-

oxidized molecule of pyrrole to give a dimeric cation (C4H4NH)2]++

. The

process repeats itself many times. Conductive forms of PPy are prepared

by oxidation (p-doping) of the polymer:

(C4H2NH)n + x FeCl3 → (C4H2NH)nClx + x FeCl2

The polymerization and p-doping can also be affected electrochemically.

The resulting conductive polymers are peeled off of the anode.

Polypyrrole is also being investigated in low temperature fuel cell

technology to increase the catalyst dispersion in the carbon support

layers [16-19] and to sensitize cathode electro-catalysts, as it has been

inferred that the metal electro-catalysts (Pt, Co, etc.) when coordinated

with the nitrogen in the pyrrole monomers show enhanced oxygen

reduction activity. Polypyrrole (together with other conjugated polymers

such as polyaniline, poly(ethylenedioxythiophene) etc. has been actively

studied as a material for artificial muscles, a technology that would offer

numerous advantages over traditional motor actuating elements [20].

Polypyrrole was used to coat silica and reverse phase silica to yield a

material capable of anion exchange and exhibiting hydrophobic

interactions. Polypyrrole was used in the microwave fabrication of multi-

walled carbon nanotubes, a new method that allows obtaining CNTs in a

matter of seconds [21]. Chemical and Engineering News reported in June

2013 that Chinese research has produced a water-resistant polyurethane

sponge coated with a thin layer of polypyrrole that absorbs 20 times its

weight in oil and is reusable.

25

Polyaniline (PAni) is a conducting polymer of the semi-flexible rod

polymer family. Although the compound itself was discovered over 150

years ago, only since the early 1980s has polyaniline captured the intense

attention of the scientific community. This interest is due to the

rediscovery of high electrical conductivity. Amongst the family of

conducting polymers and organic semiconductors, polyaniline has many

attractive processing properties. Because of its rich chemistry, polyaniline

is one of the most studied conducting polymers of the past 50 years [22].

Polymerized from the inexpensive aniline monomer, polyaniline can be

found in one of three idealized oxidation states:

Polyaniline (PAni)

In above Figure, x equals half the degree of polymerization (DP).

Leucoemeraldine with n=1, m=0 is the fully reduced state. Pernigraniline

is the fully oxidized state (n=0, m=1) with imine links instead

of amine links [23]. Studies have shown that most forms of polyaniline

are one of the three states or physical mixtures of these components. The

emeraldine (n=m=0.5) form of polyaniline, often referred to as

emeraldine base (EB), is neutral, if doped (protonated) it is called

emeraldine salt (ES), with the imine nitrogens protonated by an acid.

Protonation helps to delocalize the otherwise trapped diiminoquinone-

diaminobenzene state. Emeraldine base is regarded as the most useful

form of polyaniline due to its high stability at room temperature and the

fact that, upon doping with acid, the resulting emeraldine salt form of

26

polyaniline is highly electrically conducting. Leucoemeraldine and

pernigraniline are poor conductors, even when doped with an acid [24].

The colour change associated with polyaniline in different

oxidation states can be used in sensors and electrochromic

devices. Although colour is useful, the best method for making a

polyaniline sensor is arguably to take advantage of the dramatic changes

in electrical conductivity between the different oxidation states or doping

levels [25]. Treatment of emeraldine with acids increases the electrical

conductivity by ten orders of magnitude [26]. Undoped polyaniline has a

conductivity of 6.28×10−9

S/m, while conductivities of 4.60×10−5

S/m can

be achieved by doping to 4% HBr. The same material can be prepared by

oxidation of leucoemeraldine. Polyaniline is more noble than copper and

slightly less noble than silver which is the basis for its broad use in

printed circuit board manufacturing and in corrosion protection [27].

1.3.4 Importance of Conducting Polymers as Sensors

Conducting polymers are basically plastics which are made out of small

building blocks called monomers just like ordinary plastics but they can

conduct electricity. A common feature of conducting polymers is the

alteration of single and double bonds, at least in the backbone of the

polymer structure [28]. Polymers constitute another class of materials

which are also very promising for application in chemical sensors. In

general, polymers could be used in all types of sensors as long as they can

function at room temperature. The great advantage of conducting polymer

based sensors over other available technologies is that the conducting

polymers have the potential for improved response properties and are

sensitive to small perturbations. A large number of chemical sensors use

polymers because they offer great design flexibility [29]. The flexibility

of polymers properties, however, is attained at the expense of doping and

27

the introduction of functional additives. The primary dopants (anions)

introduced during chemical or electrochemical polymerization maintains

charge neutrality and generally increases the electrical conductivity.

Doping generates charge carriers in the polymer chain through chemical

modification of the polymer structure and involves charge exchange

between the polymer and the dopant species. The nature of the anion also

strongly influences the morphology of the polymer. In addition, anions

can serve as specific binding sites for interaction of the conducting

polymer with the analyte gas. They are relatively open materials that

allow ingress of gases into their interior. Common classes of organic

conducting polymers are acceptable for conductometric gas sensor

application.

Conducting polymers display a wide variety of properties, ensuring a vast

number of potential applications in a large number of technologies.

According to Persaud (2005), polymer based sensors have the following

advantages [30]:

i-The sensors have rapid adsorption and desorption kinetics at room

temperature.

ii-The sensor elements feature low power consumption (of the order of

microwatts), because no heater element is required.

iii-The polymer structure can be correlated to specificity toward

particular classes of chemical compounds.

iv-The sensors are resilient to poisoning by compounds that would

normally inactivate some inorganic semiconductor type sensors.

1.3.5 Ionization in Conducting Polymers

Ionization in conducting polymer is due to doping. The introduction of

charge during the doping process leads to a structural distortion of a

28

polymeric structure in the region of the charge, giving an energetically

favourable conformation. These structural distortions are intrinsic to the

development of ionization states called polarons and bipolarons.

1.3.6 Bulk and nano polymer

Polymer nanocomposites (PNC‟s) consist of a polymer or copolymer

having nanoparticles or nanofillers dispersed in the polymer matrix.

These may be of different shape (e.g. platelets, fibres, spheroids), but at

least one dimension must be in the range of 1–50 nm. These PNC‟s

belong to the category of multi-phase systems (MPS, viz. blends,

composites, and foams) that consume nearly 95% of plastics production.

These systems require controlled mixing/compounding, stabilization of

the achieved dispersion, orientation of the dispersed phase, and the

compounding strategies for all MPS, including PNC, are similar. Polymer

nanoscience is the study and application of nanoscience to polymer-

nanoparticle matrices, where nanoparticles are those with at least one

dimension of less than 100 nm. The transition from micro to nano-

particles, lead to change in its physical as well as chemical properties.

Two of the major factors in this are the increase in the ratio of the surface

area to volume, and the size of the particle. The increase in surface area-

to-volume ratio, which increases as the particles get smaller, leads to an

increasing dominance of the behaviour of atoms on the surface area of

particle over that of those interior of the particle. This affects the

properties of the particles when they are reacting with other particles.

Because of the higher surface area of the nano-particles, the interaction

with the other particles within the mixture is more and this increases the

strength, heat resistance, etc. and many factors do change for the mixture.

An example of a nanopolymer is silicon nanospheres which show quite

29

different characteristics; their size is 40–100 nm and they are much

harder than silicon, their hardness being between that of sapphire and

diamond.

1.3.7 Applications of Polymer

Due to their poor processability, conductive polymers have few large-

scale applications. They have promise in antistatic materials and they

have been incorporated into commercial displays and batteries, but there

have had limitations due to the manufacturing costs, material

inconsistencies, toxicity, poor solubility in solvents, and inability to

directly melt process. Literature suggests they are also promising

in organic solar cells, printing electronic circuits, organic light-emitting

diodes, actuators, electrochromism, super capacitors, chemical sensors

and biosensors [31], flexible transparent displays, electromagnetic

shielding and possibly replacement for the popular transparent conductor

indium tin oxide. Another use is for microwave-absorbent coatings,

particularly radar-absorptive coatings on stealth aircraft. Conducting

polymers are rapidly gaining attraction in new applications with

increasingly processable materials with better electrical and physical

properties and lower costs. The new nanostructured forms of conducting

polymers particularly augment this field with their higher surface area

and better dispersability.

1.4 Synthesis of Polymers and their Polymer Composites

Electrochemical polymerization (ECP) is performed in a single-

compartment cell containing electrochemical bath which includes a

monomer and a supporting electrolyte dissolved in appropriate solvent. It

also includes three different electrode such as working electrode

(cathode), reference electrode and counter electrode (anode). Film

30

deposited on the counter electrode (anode). Usually ECP is carried out

either Potentiostatically (i.e. constant voltage condition) or

Galvanostatically (i.e. constant current condition) by using a suitable

power supply. Potentiostatic conditions are recommended to obtain thin

films while galvanostatic conditions are recommended to obtain thick

films [32].

Chemical polymerization is the process in which relatively small

molecules, called monomers, combine chemically to produce a very large

chainlike or network molecule. The monomer molecules may be all alike,

or they may represent two, three, or more different compounds. Usually

at least 100 monomer molecules must be combined to make a product

that has certain unique physical properties such as elasticity, high tensile

strength, or the ability to form fibers that differentiate polymers from

substances composed of smaller and simpler molecules; often, many

thousands of monomer units are incorporated in a single molecule of a

polymer. The formation of stable covalent chemical bonds between the

monomers sets polymerization apart from other processes, such as

crystallization, in which large numbers of molecules aggregate under the

influence of weak intermolecular forces.

1.4.1 Preparation of Thin films

Obtaining a thin film of any material on a substrate surface with proper

adherence is thin film deposition. Deposition techniques can be broadly

classified as physical deposition methods and chemical deposition

methods. The deposition process of a film can be divided into three basic

phases:

(a) Preparation of the film forming particles (atoms, molecules, cluster)

(b) Transport of the particles from the source to the substrate

31

(c) Adsorption of the particles on the substrate and film growth

There are two type of deposition method has been involved in the

preparation of thin-films such as physical deposition method and

chemical deposition method.

Physical Deposition Methods

Physical deposition methods include several methods such as thermal

evaporation, sputtering, pulsed laser deposition and cathodic arc

deposition etc. All these methods require maintenance of vacuum of 10-6

Torr or more. Besides these deposition methods, other methods like

reactive sputtering, molecular beam epitaxy, liquid phase epitaxy etc. are

also used for obtaining improved quality of films by precisely controlling

the deposition parameters. Rate of deposition, substrate temperature,

ambient conditions, residual gas pressure in the system, purity of the

material to be deposited, in homogeneity of the films, structural or

compositional varieties of the films in the localized or wider areas

determine the electrical, optical, magnetic and surface properties of the

deposited films.

Chemical Deposition Method

Chemical deposition methods include electroplating, chemical vapour

deposition, plasma enhanced chemical vapour deposition,

organometallic solutions etc. A non vacuum technique, for producing thin

films, is the use of organometallic solutions that are applied to a substrate

surface either by dipping or by spinning or by spraying. The film is then

dried and baked in the furnace. Thermal deposition takes place and the

film is converted to pure oxide while the organic constituents evaporate.

Thickness control is achieved by adjusting the temperature, viscosity and

other properties of the solutions. This technique besides being

continuously used in materials related research has been used

32

successfully to coat high power laser optical components with anti

reflection design that have extremely high damage thresholds. In the

present thesis thin films prepared by sol-gel spin coating and spray

pyrolysis methods using organometallic solutions have been used. The

thickness of the films obtained from sol-gel spin coating and spray

pyrolysis methods lie in the range of few hundreds of nanometers.

1.4.2 Sol-gel process

Sol-gel process is a chemical deposition process which is very widely

used for the deposition of thin films, fibers, rods etc. The sol-gel

preparation of any metal oxide involves combining reactants and the

subsequent solidification of the resultant solution into an amorphous

oxide gel [33]. The porous oxide is then heated to give densified glasses

and polycrystalline solids. Incorporation of impurities and formation of

composites is easy [34-35].

The advantages of the process are ultra homogenation due to atomic scale

mixing, high degree of uniformity control on thickness, possibility of

multilayer coating and no restriction on shape and size of the substrate.

The sol-gel method is an alternative to vacuum deposition techniques.

Sol-gel process consists essentially of three steps [36-37].

(a) Formation of low viscosity solutions of suitable precursors i.e. metal

derivatives (organic/inorganic) which could finally yield the oxides or

metal oxides themselves. Low viscosity insures homogenation.

(b) Formation of a uniform sol and causing it to gel to endow chemical

homogeneity on the ceramic product during desiccation.

(c) Shaping during or after gelation into the final form fibers, surface coating

etc. before annealing.

The temperatures, pH of the medium and anions/complexing agents

present in the solution are the main factors affecting the sol-gel process.

33

The sol-gel process is used in developing thin film transistors, anti-

reflection coatings, real view mirrors, solar reflecting glass, excitonic

devices working at high temperature, transparent conducting films,

magnetic films, protective coatings, films for sensors etc [38-42].

Sol and Precursor

Precursors are the starting chemicals which are compounds of relevant

components acting as solutes in sol-gel process and they should be able to

form reactive inorganic monomers. Precursors should be soluble in the

reaction media and should be reactive enough to participate in the sol gel

forming process. The reactivity of precursor depends on its chemical

nature as well as on applied reaction conditions. Metal oxides or metal

hydroxides usually remain in the solution rendering it directly coatable on

the substrates. Variation is the viscosity or concentration of the solution

can be used to adjust the thickness of the film. When metal is not

available in a soluble form, its organic compound can be taken as a

precursor in a suitable solvent and then is made to undergo slow and

controlled hydrolysis till it provides a metal-oxygen metal network in a

sol state maintaining most of the time the solubility and transparency of

the solution. In case of metal oxide precursors the product can be easily

freed from the carbonaceous residue. However the homogeneity is

limited. Alkoxides of group I and II metals are non volatile solids and

often depict low solubility in organic solvents. As an alternative, metal

salts, which are soluble in organic solvents and can be converted easily to

the oxide by thermal or oxidative decomposition, are used.

Gelation

The transformation of fluid sols to solidified gel depends on the rheology

of the sols gelation reduces the distance between the colloidal particles

34

and bonds are formed. The transformation of the solution into a semi-

rigid wet gel can be done by-

(a) By water evaporation or extraction using tray drying, spray drying or

dispersion in an immiscible fluid

(b) By removal or neutralization at anions or

(c) By polymerization of organometallic compounds

The network forming components, monomers or colloids, react into

active forms after the preparation of a solution or a homogeneous

colloidal sol. For stable colloids the neutralization of surface charges,

aggregation and further condensation by reactive surface groups leads to

gelation. To deposit thin film sol or precursor state is used while for

fabricating fibers gel-state is used [43].

1.4.3 Sol-gel spin coating

In the sol-gel spin coating process the substrate spins around an axis

perpendicular to the coating area. The following are four distinct stages to

the spin coating process. In the first step a controlled amount of the

precursor is poured over the substrate which wets substrate uniformly. If

needed, sub-micron filter is also used to eliminate larger particles from

the precursor.

The second step involves spinning of substrate with desired rotation

speed to remove the excess fluid. The top of the fluid layer exerts inertia

while the substrate rotates at a faster speed. These two forces result in

twisting motion which may lead to formation of spiral vortices. But in

normal cases the precursor is thin enough so that it keeps co-rotating with

the substrate and any evidence of thickness difference is absent.

Ultimately the substrate reaches its desired speed and the viscous shear

drag is exactly balanced by the rotational acceleration.

35

In the third step viscous forces dominate the thinning behavior of the

fluid. The fluid thinning tends to formation of uniform films. However in

few cases edge effect are also seen. The fluid which is rotating flows

uniformly outside. If the fluid is in excess then the drops must be formed

at the edges so that they may fling off. Thus the thickness at the ends may

be slightly greater than that at the central portion of the substrate leading

to edge effect.

In the fourth and final stage fluid starts evaporating and dominates its

own thinning behavior. It is the stage in which the solvent phase gets

removed and the sol is converted to dense ceramic. As the fluid rotates at

a high speed, its temperature rises and leads to evaporation of the fluid.

Thus the viscosity of the remaining solution increases leading to the „gel-

state‟ of the coating. The resulting film usually has an amorphous

structure. Although the third and fourth stages i.e. viscous flow and

evaporation occur simultaneously, the viscous flow effect dominates

initially and evaporation dominates later.

The sol should be kept in an air tight flask to maintain its viscosity

otherwise it gets converted into gel and cannot be used for the deposition

of films [44]. The factors that affect thickness of the film are viscosity of

the coating solution, rotation rate, annealing temperature and time

duration. Gel coated films are porous and sintered when they are heated.

1.4.4 Spray pyrolysis

The chemical spray pyrolysis technique is one of the major techniques to

deposit a wide variety of materials in thin film from over a considerably

large area. In spray deposition process, a precursor solution is pulverized

by means of a neutral gas so that it arrives at the substrate in the form of

very fine droplets. The substrate is generally held at high temperature

36

where the constituents of the precursor solution react to form the desired

compound while other reaction products leave as volatile components.

The optimization of the chemical solution into a spray of fine droplets is

effected by spray nozzle with the help of a carrier gas which may not be

involved in the pyrolytic reaction. Large area uniform coverage of the

substrate is achieved by scanning either or both the spray head and the

substrate employing electromechanical arrangements. The chemicals used

for spray pyrolysis have to satisfy the following conditions:

I. The desired thin film material must be obtained as a result of thermally

activated reaction between the various species/complexes dissolved in

spray solutions.

II. The remainder of the constituents of the chemicals, including the

carrier liquid should be volatile at the pyrolysis temperature.

The spray pyrolysis technique had been used for the production of thin

films of simple oxides, mixed oxides, metal spinal type oxides, binary

and ternary chalcogenides, copper compounds and also super conducting

oxide films because they have satisfied both the above conditions. Thin

film deposition by spray pyrolysis has a number of advantages which are

enumerated below:

(a) The film properties can be easily changed by changing the generated

droplet sizes which can be done by employing different external pressures

during atomization.

(b) It offers an extremely easy way for doping and thus the cation to anion

ratio in compound materials can be easily varied by adding complexing

agents while electronic properties of the deposited thin films.

(c) Viscosity of the precursor solution and the spray rate/flow rate can be

changed for obtaining desired film thickness.

(d) Unlike closed vapour deposition methods, spray pyrolysis does not

require vacuum at any state.

37

(e) Above all this, the method offers deposition of thin films over a large area

and therefore the technique can be scaled up easily for industrial

applications.

However, the disadvantage with spray pyrolysis technique is that only a

few percent of the material supplied is deposited onto the substrate. After

atomization a large fraction of the droplets does the deposition efficiency

is low. Also there is a significant variation in the generated droplet size in

the aerosol. The aerosols generated by atomizers differ in droplet size,

rate of atomization and droplet velocity.

In spray pyrolysis decomposition, the impinging aerosols on the substrate

undergo endothermic reaction with substrate surface resulting in a

heterogeneous type of growth. Hence, there does not occur an oriented

type of growth in the first few layers. As the thickness increases the

arrangements to atoms in further layers get gradually modified by the

proceeding layers. As a result, the growth takes place in a more definite

way resulting in a film of preferred orientation.

1.4.5 Dip-coating

Sol-gel dip coating was invented in Europe in 1960. This is one of the

best and simpler coating process in which first of all the substrate to be

coated is put into the pot containing the sol of desired material suitably

tuned for gelation property. Now the substrate is taken out from this pot

at constant speed may be under controlled environmental conditions if

desired so. Special arrangement for lifting the substrate is required which

can ensure constant speed without jerks or vibrations. Generally

microprocessor controlled equipment is used these days for this purpose.

Coated film thickness depends on lifting speed, angle of substrate lifting

38

with the liquid surface and environmental conditions under which coating

procedure is carried out [45].

1.5 Characterization Techniques

The standard methods of measurement and characterizations are

constantly employed for the investigation of nanostructures.

Structural/morphological and optical properties determination and

understanding are an important and integral part of nanomaterials

research.There are a number of powerful experimental techniques that

can be used to characterize structural/morphological, surface and optical

properties of nanomaterials either directly or indirectly, e.g. XRD (X-ray

diffraction), STM (scanning tunneling microscopy), AFM (atomic force

microscopy), SEM (scanning electron microscopy), TEM (transmission

electron microscopy), IR (infrared). Some of these techniques are more

surface sensitive than others. The choice of characterization technique

depends strongly on the information being sought about the material.

Optical spectroscopy such as IR and Raman provide more direct

information about structure while UV-visible absorption spectroscopy

and photoluminescence (PL) spectroscopy provide indirect structural

information. In general optical spectroscopy is sensitive to structural

properties but cannot provide a direct probe of the structural details.

Optical properties are commonly characterized using spectroscopic

techniques including UV-visible and photoluminescence spectroscopy, as

both yield information about the electronic structure of nanomaterials.

Other characterization techniques such as TG-DTA (Thermal

Gravimetric-Differential Thermal Analysis) and FTIR (Fourier-transform

infrared) spectroscopy are also useful for polymers. In this section, the

39

characterization techniques used in the present works are discussed as

follows:

1.5.1 X-Ray Diffraction (XRD)

X-ray diffraction technique is a powerful tool for material

characterization. This technique is applied not only for structure

determination of solids but also to some other problems, such as chemical

analysis, stress measurement, study of phase equilibrium, determination

of particle size, determination of orientation of crystal. We know that the

physical properties of solids (e.g. electrical, optical, magnetic etc) depend

on atomic arrangements of materials, so the determination of the crystal

structure is an indispensable part of the characterization of materials. If a

crystalline specimen is visualized as being made up of tiny fragments of

completely random arrangement, it is called a fine crystalline powder. X-

rays are used to establish the atomic arrangement or structure of the

materials because the interplanar spacing (d) of the diffracting planes is

of the order of X-ray wavelength. For a crystal with a given d-spacing

and for a given wavelength λ, the various orders n of reflection occur

only at the precise values of angle θ, which satisfy the Bragg equation

nd sin2

The powder profile of the substance, even without further interpretation

can be used for identification of materials. The simplicity and advantage

of X-Ray powder diffraction method can be given as follows:

a) The powder diffraction pattern is the characteristic of the substance,

b) Each substance in a mixture produces its pattern independent to others,

c) It describes the state of chemical combination of elements in the

materials,

d) The method is capable to develop quantitative analysis of substances.

40

1.5.2 Scanning Electron Microscopy (SEM)

Scanning electron microscopy is used primarily for the study of surface

morphology of solid materials. An electron beam passing through an

evacuated column is focused by electromagnetic lenses onto the specimen

surface; the beam is then rastered over the specimen in synchronism with

the beam of a cathode ray tube display screen. In elastically scattered

secondary electrons are emitted from the sample surface and collected by

a scintillator, the signal from which is used to modulate the brightness of

the cathode ray tube. In this way the secondary electron emission from

the sample is used to form an image on CRT display screen.

Sample preparation for obtaining SEM

For conventional imaging in the SEM, specimens must be electrically

conductive at least at the surface and electrically grounded to prevent the

accumulation of electrostatic charge at the surface. Metal objects require

little special preparation for SEM except for cleaning and mounting on a

specimen stub. Non conductive specimens tend to have charge

accumulated on them when scanned by the electron beam which causes

scanning faults and other image artifacts. They are therefore usually

coated with an ultrathin coating of electrically conducting material,

commonly gold. It is deposited on the sample either by low vacuum

sputter coating or by high vacuum evaporation. Conductive materials in

current use for specimen coating include gold, gold-palladium alloy,

platinum, osmium, iridium, tungsten, chromium and graphite etc. Gold-

palladium alloy has been used as the coating material for the SEM

recording of the samples in the present thesis.

41

Fig. 1.6: Schematic representation of X-ray diffraction.

42

Fig. 1.7: Schematic diagram of SEM.

43

1.5.3 Fourier Transformed Infrared Spectroscopy (FTIR)

The FTIR spectroscopy is a powerful modern technique in which

spectrum is first produced as an interferogram which is processed and

computed in real time through a dedicated computer to provide high

resolution information. Infrared spectroscopic studies are carried out.

Polyaniline samples with different dopant ions are analysed by using

Fourier transform infra-red spectrometer (Model-430, LEO Cambridge,

England). Infrared spectroscopy provides information about the

concentration of the impurities, and their bonding with the host material.

In FTIR, the infrared radiation is split into two beams, out of which one is

kept static and the other moving. These are combined to give a modulated

beam which is passed through the sample. It is then digitized and Fourier-

transformed by the computer to give the infrared spectrum. For analysis

of the data, standard spectra of bulk powder and used evaporation source,

which are mixed with pure and dry KBr powder processed into thin

pellets, are recorded. The schematic representation of FTIR is shown in

Fig. 1.8.

Atmospheric moisture and carbon dioxide can cause problem in infrared

spectra. Water absorbs around 4000 to 3500 cm-1

and 2000 to 1300 cm-1

,

while carbon dioxide absorbs at 2350 and 688 cm-1

. This absorbance

often mask weak feature that are of interest for a particular investigation.

Purging with dry air or nitrogen and annealing treatments are performed

prior to loading the film for FTIR spectra investigation. FTIR

spectroscopy has following applications:

(a) Useful spectral information can be obtained from a sample of a

microgram or less. Utilizing special techniques, as little as 50 picograms

may be analysed.

44

(b) A spectrum can be obtained in much shorter time than is possible with

a dispersive spectrometer. Thus, spectra can be obtained to transient

species or phenomenon down to as short a time as 1/30th

of a second.

(c) A combination of both those advantages make it possible to obtain

infrared spectra of gas chromatographic and high pressure liquid

chromatographic cuts as they emerge from the chromatograph, thus

providing considerable structural about the material giving rise to each

peak in the chromatograms.

(d) The spectrum can be obtained at very high resolution, which has

certain advantages in studying small molecules in vapour phase.

(e) Utilizing microscope accessories, spectra of individual particles or

inclusions of the order of 5µm in size can be obtained.

1.5.4 UV-Visible Spectroscopy

UV-visible absorption spectroscopy is the widely used method of optical

characterization such as studying the band gap of semiconductor

materials; identifying some functional group, assaying and determination

of content as well as strength of substance. In UV-visible absorption

spectroscopy, absorption spectra are recorded with UV-vis double beam

spectrophotometer in a 1 cm path length quartz cuvette after

ultrasonification of colloidal solution to disperse the particles. The

spectrophotometer is equipped with two continuous light sources (i) a

hydrogen or deuterium lamp for measurement in ultraviolet range and (ii)

a tungsten or halogen lamp for the measurement in visible range (1000

nm to 400 nm). In this way, radiation across the whole range is scanned

by the spectrophotometer. The schematic representation of UV-visible

absorption spectroscopy is shown in Fig. 1.9 (A). In brief, a beam of light

from a visible and/or UV light source is separated into its component

wavelengths by a prism or diffraction grating. Each monochromatic

45

(single wavelength) beam in turn is split into two equal intensity beams

by a half-mirrored device. The sample beam passes through a sample

cuvette containing a solution of the compound being studied in a

transparent solvent. The reference beam passes through an identical

reference cuvette containing only the solvent. The intensities of these

light beams are then measured by electronic detectors and compared.

Over a short period of time, the spectrometer automatically scans all the

component wavelengths in the manner described. The ultraviolet (UV)

region scanned is normally from 200 to 400 nm, and the visible portion is

from 400 to 800 nm. Generally, Photomultiplier tube (PMT) or

Semiconductor Photodiodes or Charge Coupled Devices (CCD) can be

used as a detector.

1.5.5 Photoluminescence (PL) Spectroscopy

It is a powerful technique for extracting information about the electronic

structure of the material from the spectrum of light emitted. At room

temperature (RT) there is a non-zero occupancy of electron states near the

bottom of the conduction band and hole states near the top of the valence.

Hence, electron-hole pairs can recombine to emit photons over a range of

energies, producing a broad band rather than a sharp peak. Donor,

acceptor and defects states are generally fully ionized at room

temperature and do not contribute significantly to the observed spectrum.

These problems can be avoided by recording photoluminescence spectra

at low temperature in which the sample is enclosed in a cryostat and

illuminated with above band gap source. The most basic use of low

temperature PL spectra is as an indicator of overall crystal quality. The

crystal quality is indicated by two factors: first the ratio of excitonic

luminescence to donor-acceptor and deep level luminescence, second the

sharpness of the spectrum i.e. the extent to which adjacent lines can be

46

resolved. Apart from indicating overall crystal quality, the low

temperature PL can sometimes be helpful in identifying specific

impurities. The schematic representation of photoluminescence

spectroscopy is shown in Fig. 1.9 (B).

Fig. 1.8: The schematic representation of FTIR spectroscopy.

47

Fig. 1.9: Schematic representations of (A) UV-visible absorption

spectroscopy and (B) photoluminescence Spectroscopy.

48

1.6 Objective of present work

The main objective of present work is to synthesize different conducting

polymer and their polymer composites for study the structural,

morphological and optical properties for various device applications. In

whole work, polythiophene, polyaniline and polypyrrole have been used

as host materials in form of pellets and thin films. The different dopants

such as Al2O3, CuO and TiO2 have been used to improve the properties of

synthesized conducting polymer. The study focuses on the following

objectives:

(a) To synthesize undoped and Al2O3 doped polythiophene by chemical

method and their pelletization. The structural, surface morphological and

optical characterizations are done so as synthesized materials of optimum

quality

(b) To synthesize undoped and CuO doped polyaniline by chemical

method and their pelletization. The structural, surface morphological and

optical characterizations are done so as synthesized materials of optimum

quality

(c) To synthesize undoped and Al2O3 doped polypyrrole by chemical

method and their pelletization. The structural, surface morphological and

optical characterizations are done so as synthesized materials of optimum

quality

(d) To synthesize undoped and Al2O3 doped polyaniline by chemical

method and sol-gel dip coating films. The structural, surface

morphological and optical characterizations are done so as synthesized

materials of optimum quality

49

(e) To synthesize undoped and TiO2 doped polypyrrole by chemical

method and sol-gel spin coating thin films. The structural, surface

morphological and optical characterizations are done so as synthesized

materials of optimum quality

(f) To perform the structural, surface morphological and optical studies

so as to obtain thin films of optimum quality.

1.7 Organization of present work

The content of the present thesis has been divided into seven chapters.

Chapter 1: It gives the introduction to the subject. Deposition and various

characterization methods of pellets and thin films are described.

Chapter 2: The chapter 2 presents the synthesis and characterization of

Al2O3 doped polythiophene by chemical oxidation method and their

pelletization and their characterization using X-ray study, SEM, FTIR

spectroscopy and PL spectroscopy.

Chapter 3: This chapter deals with the synthesis and characterizations of

CuO doped polyanilne by chemical oxidation method and their

pelletization. The structural, morphological and optical characterizations

are also present.

Chapter 4: This chapter deals also with the synthesis and characterization

of undoped and Al2O3 doped polypyrrole by chemical oxidation method

and their pelletization. Their characterizations have been done using

XRD, SEM, FTIR, UV-Vis and PL.

Chapter 5: The chapter 5 presents structural, morphological and optical

study of undoped and Al2O3 doped polyaniline by chemical oxidation

50

method and sol-gel dip coating thin films. Their characterizations have

been done using XRD, SEM, FTIR, PL and transmission.

Chapter 6: Structural, morphological and optical study of undoped and

TiO2 doped polypyrrole by chemical oxidation method and sol-gel spin

coating thin films is presented in Chapter 6. The structural,

morphological, FTIR and optical characterizations are also present.

Chapter 7: Conclusions of the present work are presented in chapter 7

along with the recommendation for further work.

51

Chapter 2

Synthesis and Characterization of Undoped and Al2O3

Doped Polythiophene Nanocomposites

2.1 Introduction

Currently, conducting polymers (CPs) such as polypyrrole (PPy),

polyaniline (PAni), polythiophene (PTh) and their derivatives are

promising materials for the synthesis of nanocomposites (NCs) material

and their device applications. Among conducting polymers composites,

the polythiophene– metal oxide composites have received much more

attention from scientific communities and researchers in recent years

because of their unique electrical, electrochromic and electronic

properties with high environmental and thermal stabilities [1-3]. The

polythiophene–metal interfacial structure is very important issue for

various scientific and technological points of view. It is one of the

important and most frequently used CPs in the industries with wide range

of potential applications including chemical and optical sensors, light-

emitting diodes (LEDs), display devices, photovoltaic solar cells and

transistors [4-5]. However, characterization, processing and applications

of this class of materials have been limited by the poor solubility in

organic solvents. Initially, the synthesized CPs was insoluble and

infusible because of their strong inter-chain interactions. These two

features are extremely disadvantageous for basic research and

technological applications [6-7]. This inherent insolubility also greatly

hinders the understanding of their molecular properties. In-spite of above

problems with PTh, efforts are being made to improve its solubility with

organic acids by concerning protonation. The soluble CPs is synthesized

by chemical oxidative polymerizations, electro-polymerizations and

52

metal-catalyzed coupling reactions [8]. Currently a new class of materials

emerged, known as composites, synthesized by mixing suitable organic

and inorganic base materials in proper proportions. The composite

materials have their unique properties but in some of the cases, it can also

have other desirable properties of both the parent organic and inorganic

materials. As a result, there are increasing interests in combing both

organic and inorganic materials for device applications. The research on

polymer based nanocomposites (NCs) are one of the most flourishing

field in material science owing to their potential applications such as

electrochemical, mechanical, magnetic and dielectric properties [9].

Aluminium oxide is a chemical compound of aluminium and oxygen with

the chemical formula Al2O3. It is also called alumina. It has a wide

bandgap of ~8.8 eV for bulk material. It is an electrical insulator but has a

relatively high thermal conductivity around 30 Wm−1

K−1

for a ceramic

material. Aluminium oxide is insoluble in water. Al2O3 has been

extensively investigated dopants to serve as catalysts, fire redundant,

absorbents and fillers for structural materials [10]. It is stable in acidic

and oxidative mediums and well known for reactivity with aromatic

organic materials.

In this chapter an attempt is made to synthesize undoped PTh and

Al2O3/polythiophene NCs via chemical oxidation method and their

optical properties are studied. The doping of Al2O3 enhances the optical

properties of the polythiophene and therefore, UV-vis absorption

spectroscopy, FTIR and PL measurements have been investigated in

details.

53

2.2 Experimental

2.2.1 Chemicals

The cetyltrimethylammonium bromide (CTAB, 1.64 gm),

triethanolamine (TEA, 13.18 gm), thiophene and ammonium persulfate

(APS, 8.26 gm) were obtained from Aldrich. These chemical were of

high purity (99.999%) with analytical grade and were used directly

without special treatment.

2.2.2 Sample preparation

Cetyltrimethylammonium bromide (CTAB, 1.64 gm), triethanolamine

(TEA, 13.18 gm) and thiophene are dissolved in deionized water in a

flask (Sol-A). The mixture solution (designated as Sol-A) was placed in

ultrasonic bath for 30 min. Ammonium persulfate (APS, 8.26 gm) was

dissolved in 20 ml de-ionized water and formed solution (Sol-B). The

Sol-B was added drop-wise into Sol-A. The mixture of Sol-A and Sol-B

was heated without stirring for 24 h at 70 0C. The resulting precipitate

was collected by filtration and then washed several times by de-ionized

water and methanol. Finally obtained precipitate was dried in air for 30

min and then placed in oven for 3 h at 60 0C. The resulted product of

polythiophene was in form of powder with brown colours. The

synthesized polythiophene was doped with Al2O3 in the proper proportion

of 2, 4, 6 and 8 wt%. The undoped and doped polythiophene was ground

into make fine powders. Pellets are prepared by compressing the powder

under a pressure of 10 tons with the help of a hydraulic press machine.

All the pellets were annealed at 150 0C for 1 hour. The diameter of the

pellets was found to be 13 mm.

54

2.2.3 Characterizations

The XRD spectra of all the samples recorded by Phillips X’pert PW3020

diffractometer using CuKα radiation (λ=1.54056 Ao) were presented for

structural analysis of the samples. The SEM images of all the pellets were

taken by scanning electron microscope (Model-430, LEO Cambridge,

England). FTIR spectra of all the samples in the form of powder were

recorded on the Bruker Alpha spectrometer to determine the formation of

polythiophene. To record absorbance spectra, 0.01 gm of each sample is

dissolved in 5 ml of dimethyl formamide (DMF). Then the absorption

spectra of the solutions thus formed were recorded with UV-vis

spectrophotometer (Model No.V-670 Jasco). PL spectra of all the

samples were recorded using LS-55, Perkin Elmer fluorescence

spectrometer at room temperature with excitation wavelength (λexc.) 325

nm.

2.3 Results and discussion

2.3.1 Structural study

Fig. 2.1 shows the X-ray diffraction (XRD) patterns of undoped PTh and

Al2O3/ PTh nanocomposites. For undoped sample ‘a’ exhibits only single

peak at 2θ = 20.910 corresponding to (001) plane and four peaks along

(001), (120), (111) and (110) planes are clearly observed in doped

samples which indicate that all the samples are polycrystalline in nature

and confirmation of synthesis of polythiophene. Some additional peaks of

PTh are also seen in doped samples indicates doping effect of low

percentage of Al2O3 dopants on the lattice structure of PTh. After doping

these peaks are found to have shifted, particularly the peak appearing at

20.910 in undoped polythiophene sample which may be attributed to the

modification of crystal structures after doping [11-12]. The diffused

diffraction maxima and line broadening confirms the formations of

55

nanometre-sized particles. It is well established that during doping

processes of metal-oxides in polythiophene, it undergoes interfacial

interaction with metal crystallites and losses their original morphology.

The sample doped with 8 wt.% Al2O3 tends to change the polycrystalline

nature into single crystalline nature. XRD results indicate the weak

crystalline quality. It is evidenced from XRD results that with increase of

Al2O3 percentage, the crystallinity of prepared PTh samples are also

improved. None of the XRD patterns show any evidence of Al2O3 or

other impurity phase. The crystallite sizes of all the samples are

calculated using Debye–Scherrer’s (DS) formula:

cos

ktDS ,

Where tDS is the crystallite size, λ is the wavelength of radiation used, θ

is the Bragg’s angle and β is the full-width at half-maximum (FWHM)

measured in radian. The average crystallite size of all the samples lies in

the range between 22 to 34 nm.

2.3.2 Morphological study

The SEM is used to study the surface morphology of as-synthesized

samples. The SEM micrographs of as-synthesized samples of pure

polythiophene and Al2O3/PTh nanocomposites are shown in Fig. 2.2.

Figure shows the formation of spherical shape of nanostructures. As-

synthesized samples of undoped polythiophene and Al2O3/PTh

nanocomposites exhibit many pores on the surface of nanostructures. The

formations of spherical shaped nanostructures during polymerization

process are investigated [13] with schematic representation. In these

schematic, during occurrence of polymerization, the surfactant CTAB

forms micelles in the starting of reaction. When ammonium persulfate is

added to the solution of CTAB and triethanolamine (TEA), some white

56

precipitate appears immediately. It is found that the colour of white

precipitate gradually changed into black after few minutes. The

precipitate (CTA)2S2O8 forms lamellar meso-structure and provides

templates for polymerization that plays an important role in the

morphology transformation of PTh [14]. Furthermore, the monomer is

polymerized by the anion of (CTA)2S2O8 and form a sheet like structures.

The lamellar inorganic/organic meso-structure based templates form

during polymerization of surfactant cations with oxidizing anions which

further degraded automatically after polymerization process done. During

polymerizations, some enlarge holes are appeared on the surface which

forms a unique ‘sphere-fibre-transition’ like structures. Such type of

structure formation during polymerization is concentrated and then

broken into the spherical shaped nanoparticles during secondary growth

[15]. These transformations are outlined as shown in Scheme 1.

The number and size of pores increases with increasing doping

percentage of Al2O3.These pores are very useful in sensing properties.

The change in morphology can be explained by the adsorption and

intercalation of polythiophene on the surface of Al2O3. As a result of this

absorption process, Al2O3 are finely coated with polythiophene particles

by polymerization of thiophene monomers. Thus, it is aptly believed that

adsorption probability of thiophene monomer on the whole surface of

Al2O3 is equipotent, resulting in the formation of continuous

polythiophene coating on the surface of Al2O3 [16]. Therefore, due to the

change in surface morphology, porosity of the PTh increases with the

addition of Al2O3.

57

Scheme 1: Schematic representations of the proposed mechanism of

forming spherical polythiophene.

58

Fig. 2.1: X-ray diffraction patterns of (a) undoped PTh and Al2O3-doped

with (b) 2 wt%, (c) 4 wt%, (d) 6 wt% and (e) 8 wt% PTh nanocomposites.

59

Fig. 2.2: SEM images of the (a) undoped PTh and, Al2O3-doped with (b)

2 wt%, (c) 4 wt%, (d) 6 wt% and (e) 8 wt% PTh nanocomposites.

60

2.3.3 Optical properties

Fourier Transform Infrared Spectroscopy

In order to observe the nature of bonding in the prepared samples, we

investigated FTIR transmission spectra of pure polythiophene and Al2O3/

PTh nanocomposites are shown in Fig. 2.3. The FTIR spectra of all the

samples show strong absorption band in the range of 500-3200 cm-1

,

which correspond to the characteristics of polythiophene [17]. It is similar

to the reported standard FTIR results of polythiophene and quite different

from that of monomer based thiophene. This result further confirms the

successful polymerization of thiophene monomer and the formation of

polythiophene [17], which is well evidenced in XRD and SEM results.

The absorption bands appearing in the range of 600-800 cm-1

indicate

singly substituted benzene ring [18]. The peak located at around 1064 cm-

1 that can be assigned to the C-H in plane bending vibrations and its

intensity increases with incorporation of Al2O3. In addition, the shift in

peak position towards lower wave number up to 1053 cm-1

is also

observed after incorporation of 4 wt.% Al2O3 [1]. The peak appeared at

1433 cm-1

in pure polythiophene is attributed to υ cycles [1] which

changes after incorporation of Al2O3.

The broad peaks in FTIR spectra present at 1635 cm-1

and 3208 cm-1

are

associated with aromatic C=C stretching and C-H stretching, respectively

[1]. Additional peak at 2919 cm-1

is observed in the samples doped after 4

wt.% Al2O3 which may be attributed to C-H inplane-bending. The large

descending base line in the spectral region of 4000-2000 cm-1

is attributed

to the free-electron conduction in the doped polymer [19]. The observed

bands shifts in undoped polythiophene and appearance of extra bands in

Al2O3/PTh composites samples indicate formation of complexes between

Al2O3 molecule and polythiophene [1].

61

Fig. 2.3: FT-IR spectra of (a) undoped PTh, and Al2O3-doped with (b) 2

wt%, (c) 4 wt%, (d) 6 wt% and (e) 8 wt% PTh nanocomposites.

62

UV-visible absorbance spectroscopy

Fig. 2.4 shows the UV-visible absorption spectra of undoped

polythiophene and Al2O3/PTh nanocomposites at room temperature. The

obtained spectra are recorded with base line correction by

spectrophotometer in the wavelength ranges 200-900 nm. The absorption

spectra of all the samples exhibit absorption peak at around 300 nm

which is due to π- π* inter-band-transition of PTh rings. In this study,

small change in optical absorption spectra is observed which can be

associated with the degree of oxidation [20-21]. The change in optical

absorption spectra after doping of Al2O3 in polythiophene indicates

interaction between the Al2O3 and polythiophene [22].

Photoluminescence study

Photoluminescence is one of the suitable techniques to determine the

crystalline quality and the presence of impurities/defect states lies inside

the materials as well as exciton fine structures [11]. Generally,

polythiophene based sample exhibits optical emission in the half oxidized

states under solid form [23]. Fig. 2.5 illustrates the photoluminescence

spectra of undoped as well as Al2O3/PTh nanocomposites. In the PL

spectra of undoped and Al2O3/PTh nanocomposites, we observed mainly

three visible emission peaks centred at around 462 nm, 490 nm and 522

nm. The two emission peaks 462 nm and 490 nm in the Soret band region

where as single peak at 522 nm in the Q band emission [24]. The blue-

green emission peak at 490 nm may be originated from the side-chains.

PL intensity of polythiophene nanocomposites are rarely affected by self-

absorption due to the presence of thin shell layer of polythiophene. The

PL spectra of the polymers were almost the same, which indicates that

there is intramolecular energy transfer of the excitons from the

conjugated side chain to the main chain [25].

63

Fig. 2.4: UV-visible absorbance spectra of (a) undoped PTh, and Al2O3-

doped with (b) 2 wt%, (c) 4 wt%, (d) 6 wt% and (e) 8 wt% PTh

nanocomposites.

64

Fig. 2.5: Photoluminescence (PL) spectra of (a) undoped PTh, and Al2O3-

doped with (b) 2 wt%, (c) 4 wt%, (d) 6 wt% and (e) 8 wt% PTh

nanocomposites.

65

2.4 Conclusion

Undoped and Al2O3/polythiophene nanocomposites have been

synthesized by chemical oxidation method. The samples are characterized

by XRD, SEM, UV-vis, PL and FTIR spectroscopy. XRD spectra show

the polycrystalline nature of all the samples. SEM images are indicating

formation of spherical shape of nanostructures. As-synthesized samples

of undoped polythiophene and Al2O3/PTh nanocomposites exhibit many

pores on the surface of nanostructures. Synthesis of Al2O3/polythiophene

composite material is confirmed by FTIR spectroscopy. UV-visible

absorption spectra show absorption peak at around 300 nm which is due

to π- π* inter-band-transition of PTh rings. A small change in optical

absorption spectra is observed which can be associated with the degree of

oxidation. PL spectra exhibit mainly three visible emission peaks at

around 462 nm, 490 nm and 522 nm. The two emission peaks 462 nm and

490 nm in the Soret band region where as single peak at 522 nm in the Q

band emission. The intensity and peak position of polythiophene have

been randomly changed with amount of Al2O3 dopant.

66

Chapter 3

Synthesis and Characterization of Chemically Synthesized

Undoped and CuO Doped Polyaniline Nanocomposites

3.1 Introduction

Polyaniline (PAni) is one of the most studied conducting polymers known

to date because of it is relatively cheap, easy to synthesise and very stable

under a wide variety of experimental conditions. Like other classes of

conducting polymers, polyaniline is also easy to handle and can be

readily processed into polymeric blends [1]. Intrinsically conducting

polymer nanocomposites have been used in various kinds of electronic

devices.Conducting polymers are combined with metal oxides because of

their enhanced physical and electronic properties and find useful

applications in various devices such as sensors, electrodes, batteries and

photovoltaics [2]. Polymer-metal composites are attracting considerable

attention of the researchers due to their striking advantageous properties

such as easy processing flexibility and light weight [3] etc. Metal oxides

such as ZnO, CdS, Al2O3, TiO2 and CuO have attracted much attention to

researchers and scientific communities due to their potential applications

in electrical, optical and optoelectronics devices. Among these metal

oxides, cupric oxide (CuO), a versatile semiconductor material, has been

attracting attention because of the commercial demand for optoelectronic

devices operating at blue and ultraviolet regions [4]. Cupric oxide (CuO)

has been a hot topic among the studies on transition metal-oxides (MOs)

because of its interesting properties as a p-type semiconductor with

narrow band gap energy of 1.5–1.8 eV [5-6]. It has very large excitation

binding energy (60 meV) at room temperature [5-6]. CuO has recently

due to its exotic properties and wide applications from

67

heterogeneouscatalysts, gas sensors [7, 8], field-emission emitters to high

temperature superconductors [9], magnetic storage media [10], solar

cells, lithium ion electrode materials, catalysis [11,12] and field emitters

[13] and etc. [14, 15] because it has good mechanical flexibility and

environmental stability as well as its resistivity could be controlled with

acid/base (doping/undoping), it has application in various areas, such as

light weight battery electrode, electromagnetic shielding device,

anticorrosion coatings, solar cells, photodetectros and sensors [16–19].

As one of the important metal oxides, cupric oxide (CuO) is frequently

used as anode materials due to its high capacity, environmental friendly,

safety and low-cost [20-22]. Therefore, the preparation of composite of

polyaniline and metal oxide becomes a novel challenge for people. CuO

is stable in the acidic and oxidative environments while polymerizing

aniline together with low cost. CuO could therefore be a good candidate

as seed to fabricate different PAni/CuO nanostructures targeting at

different physiochemical properties. In the present chapter, PAni and its

composite with CuO have been synthesized successfully by chemical

oxidation method. X-ray diffraction (XRD) results show the

polycrystalline nature of prepared samples. The crystallinity of composite

materials is found to increase with increasing doping percentage of CuO.

The shifting of some bands and appearance of some extra bands in FTIR

results of doped samples with respect to undoped PAni [23-26] have been

discussed in the present chapter.

68

3.2 Experimental

3.2.1 Pellet Preparation

Aniline hydrochloride (2.59 gm) was dissolved in distilled water in a

volumetric flask to make 50 ml solution. Ammonium peroxydisulfate

(5.71 gm) was dissolved in water also to make 50 ml of solution. Both the

solutions were kept for 1 hour at room temperature. They were then

mixed with a brief stirring and left at rest to polymerize. The solution

turned to dark green within few minutes. Next day Polyaniline (PAni)

precipitate was collected on a filter paper, washed three times with 100

ml portions of 0.2M HCl to remove the unreacted aniline and its

oligomers from the precipitate. After this process, precipitate was washed

three times with 100 ml portions of acetone to absorb the water molecules

and for the removal of any residual organic impurities. PAni, synthesized

by this method, is formed in its protonated state. The precipitate was

firstly dried in air for 30 min and then in oven for 3 hours at 60°C [27].

The synthesized PAni has been doped by CuO in ratio of 2, 4, 6 and 8

wt%. The undoped and CuO doped PAni composite was ground in form

of fine powder. Pellets were prepared by compressing the powder under a

pressure of 10 tons with the help of a hydraulic press machine. All the

pellets were annealed at 100°C for one hour. The thickness of the pellets

of composite samples was found to be 0.65 mm.The diameter of the

pellets was also found to be 13 mm. The 0, 2, 4, 6 and 8 wt% CuO doped

PAni composite are denoted as samples a, b, c, d and e respectively.

3.2.2 Characterizations

X-ray diffraction (XRD) spectra of all the samples recorded by Phillips

X’pert PW3020 diffractometer using Cu Kα radiation (λ=1.54056 Ao)

were presented for structural analysis of the samples. The scanning

69

electron microscopy (SEM) images of all the sample pellets were taken

by scanning electron microscope (Model-430, LEO Cambridge,

England). FTIR spectra of all the samples in the form of powder were

recorded on the Bruker Alpha spectrometer to determine the formation of

Polyaniline. To record absorbance spectra, 0.01 gm of each sample is

dissolved in 5 ml of dimethyl formamide (DMF). The UV-visible

absorption spectra of the samples were recorded with UV-vis

spectrophotometer (Model No.V-670 Jasco) and PL spectra of all the

samples were recorded using LS-55, Perkin Elmer fluorescence

spectrometer at room temperature with excitation wavelength (λexc.) 325

nm.

3.3 Results and discussion

3.3.1 X-ray Diffraction

XRD spectra of the pure PAni and the CuO mixed PAni composite

samples a, b, c, d, and e (Fig. 3.1) show the weak crystalline quality of all

the samples. There is a main peak around at 2θ = 260 in sample a while at

around 290 in samples b, c, d and e, which correspond to (100) and (110)

planes respectively [28]. There is no peak for the cupric oxide in the

composite samples, which indicates that the low percentage of CuO does

not affect the lattice structure of PAni, similar type of result has been

reported in literature [27]. Thus the XRD spectra suggest that during the

doping of metal oxides in PAni, it undergoes interfacial interactions with

metal crystallites and losses its own morphology. The crystallite size can

be estimated with the help of full width at half maximum (FWHM) of the

X-ray diffraction data. The broadening of the FWHM is inversely

proportional to the average crystallite size, D, as predicted by the well-

70

known Scherer's formula. The crystallite size, D, is calculated from the

following relation [29]:

D = kλ/β cosθ

where, λ is the X-ray wavelength; k, the shape factor; D, the average

diameter of the crystals in angstroms; θ, the Bragg angle in degree; and β

is the line broadening measured by half-height in radian. The value of k

depends on several factors including the miller index of the reflection

plane and the shape of crystal. If the shape is unknown, k is often

considered to be 0.89. The crystallite size of PAni/CuO nano-composites

is formed to lies between 20 to 50 nm.

71

Fig 3.1: X-ray diffraction spectra for the samples a, b, c, d and e, curves

correspond to 0, 2, 4, 6 and 8wt% CuO doped PAni nanocomposites

respectively.

72

3.3.2 Scanning Electron Microscopy

Scanning electron microscope (SEM) is used to study the surface

morphology of the prepared samples. SEM images of the samples show

the formation of spongy structures as shown in Fig. 3.2, which are almost

the same for all the undoped and PAni/CuO nanocomposite samples.

Figure 3.2 (a–e) corresponds to 0, 2, 4, 6, and 8 wt % CuO and PAni/CuO

nanocomposites respectively. The spongy structure formation in the

polyaniline takes place by heterogeneous nucleation. As a result, granular

coral like structures are formed. As a characteristic of polyaniline,

secondary nucleation also takes place because of which the granular coral

like particles come together to form aggregates [29]. We noticed that as

the amount of CuO was increased; the number of pores and the size of

pores were also increased, which is very important for sensing properties.

The change in morphology can be explained by the adsorption and

intercalation of PAni on the surface of CuO. There is another possibility

that the CuO is sandwiched between the PAni layers or CuO uniformly

mixed into the PAni matrix [30-31]. The aniline monomer is likely to be

absorbed onto the surface of CuO through electrostatic attraction and by

the formation of weak charge-transfer complexes between aniline

monomer and the structure of CuO [29]. As a result of this absorption

process, CuO are finely coated by PAni particles by the polymerization of

aniline monomer. Thus, it is suitably believed that adsorption probability

of aniline monomer on the whole surface of CuO is equipotent, which

results in the formation of continuous PAni coating on the surface of

cupric-oxide. Therefore, the change in surface morphology causes the

porosity of the PAni which increases with the addition of the CuO.

73

Fig. 3.2: Scanning electron microscope (SEM) images of samples a, b, c,

d and e images a, b, c , d and e correspond to 0, 2, 4, 6 and 8 wt% CuO

doped PAni nanocomposite respectively.

74

3.3.3 Optical properties

Fourier Transform Infrared (FTIR) spectroscopy

Fourier transform infrared (FTIR) spectra of all the samples of undoped

PAni and PAni/CuO nanocomposite at different wt% are obtained in the

absorbance range 500–4000 cm-1

which are shown in Fig 3.3. The

vibrational bands observed for undoped PAni and PAni/CuO

nanocomposite are explained on the basis of normal modes. FTIR Spectra

of all the samples of undoped PAni and PAni/CuO nanocomposite show

strong absorption bands in the region 805–1591cm-1

which correspond to

the characteristics of polyaniline. The absorbance band at around 805 cm-

1 observed for undoped PAni and PAni/CuO nanocomposite samples

show characteristics peaks of the C-H out-of plane bending vibration of

the 1, 4-distibuted benzene ring. The observed peak around 1143 cm-1

for

undoped PAni and PAni/CuO nanocomposite C-H bending vibration and

observed peaks around 1309 cm-1

C-N stretching vibration for undoped

PAni and PAni/CuO nanocomposite [32]. The observed peak around

1475 cm-1

is attributed to stretching vibration of C=C of the benzenoid

ring. The absorption peaks observed around 1591 cm-1

is attributed to

C=C stretching vibration of the quinoid ring form doped PAni and

PAni/CuO nanocomposite [29].The observed peaks around at 2338 cm-1

,

3740 cm-1

for the undoped PAni and different weight percentage of

PAni/CuO nanocomposite can be probably related to the valence

oscillation of the C-H and N-H bond stretching within the benzene rings,

which have been associated with electrical conductivity and high degree

of electron delocalization in PAni [33]. The splitting and intensity of

absorption band on increasing the CuO weight percentage [Fig. 3.3 (b-e)]

suggest the presence of higher extent of protonation in these samples.

75

UV-visible Absorption Spectra

The UV–visible absorption spectra of the undoped PAni and the

PAni/CuO nanocomposite are recorded at room temperature by using a

spectrophotometer between the wavelength range 200–800 nm as shown

in Fig.3.4. Optical spectroscopy is an important technique to understand

the conducting states corresponding to the absorption bands of inter and

intra gap states of conducting polymers. Fig.3.4 illustrates the major

absorption peaks at around 305 nm. The observed bathochromic shift at

the intense band 305 is due to the π-π* transition of benzenoid ring which

is related to the extent of conjugation between the adjacent phenylene

rings in the polymeric chain and the forced planarization of π-system

induced by aggregation.It leads to increased conjugation and thus lowers

the band gap which is well agreed with the band gap result obtained in the

Polyaniline. The transition of π-π* of benzenoid ring and the formation of

polaron band in the nanocomposites are responsible for increase of the

electrical conductivity of the nanocomposite [28, 33]. Fig 3.4

demonstrates the high intense blue shift of absorption peaks of PAni from

its actual position in PAni/CuO nanocomposite which indicates that the

addition of CuO filler particles in the polyaniline matrix has large

influence on absorption spectra in the PAni/CuO nanocomposite [35, 36].

As seen in Fig 3.4 a, b, c, d and e as the dopant percentage increases the

absorbance peaks is decreases due to hypochomic effect [37].The

difference between the two spectra is due to the presence of an electron

with drawing sulfonic group in the complex and therefore the transition

band is observed at a lower wavelength.

76

Fig. 3.3: Fourier transform infrared (FTIR) spectra for the sample a, b, c,

d and e curves a, b, c, d and e correspond to 0, 2, 4, 6, and 8wt% CuO

doped PAni composite respectively.

77

Fig. 3.4: UV–visible absorption spectra for the samples a, b, c, d and e at

room temperature. Curves a, b, c, d and e correspond to 0, 2, 4, 6 and 8 wt

% CuO and PAni/CuO composites respectively.

78

Photoluminescence Studies

Photoluminescent organic molecules are a new class of compounds with

interesting properties. They undergo emission over a wide range from the

violet to the red. They can also be combined in several different forms to

produce white light. One category of organic material with

photoluminescence properties is conjugated organic polymers. PL spectra

were measured for all the four samples in the range of 300-650 nm and

the wavelength of excitation chosen for all the samples is 325 nm. The

photoluminescence spectroscopy (PL) of CuO doped PAni has been

performed and spectra is shown in Fig. 3.5. The PL spectra of 0, 2, 4, 6

and 8 wt% CuO doped PAni samples show peaks in visible region around

at 362 nm, 405 nm, 459 nm, 486 nm and 528 nm. The relative heights of

the emission peaks alter with different dopant concentrations and nature

of solvents is due to polarity. In addition, this peak becomes sharp and

intense which may be due to inter-chain species that plays an important

role in the emission process of conjugated polymers [38]. The intensity of

peaks depends on factors such as polymer coil size the nature of polymer-

solvent, polymer-dopant interactions, and the degree of chain overlapping

[38]. The PL spectra of all the samples have the same shape, which

indicates that it is an efficient way to tune the intensities of the peak by

employing specific dopant with different wt% at different concentration

levels. Overall, it is clear that the nature of conjugated polymer

aggregation depends upon many factors, including the polymer coil size,

the nature of polymer–solvent and polymer–dopant interactions and the

degree of chain overlapping [39].

79

Fig. 3.5: Photoluminescence (PL) spectra for the samples a, b, c, d and e

at room temperature. Curves a, b, c, d and e correspond to 0, 2, 4, 6 and 8

wt % CuO and PAni/CuO composites respectively.

80

3.4 Conclusion

In this chapter, we have synthesized undoped and CuO/PAni

nanocomposites by the chemical oxidation method at room temperature.

The prepared samples have been characterized by XRD, SEM,UV-vis,PL

and FTIR. XRD spectra show weak crystalline quality of all the samples,

whereas the PAni synthesized is amorphous in nature. The scanning

electron microscopy (SEM) images of all the samples show granular coral

like structure. The study of FTIR spectra confirm the formation of

conducting PAni and also suggests that doped of CuO in PAni does not

affect the structures. The UV–visible absorption spectra of the solutions

of all the samples contain some peak at 305 nm.The observed

bathochromic shift at the intense absorption band 305nm is due to the π-

π* transition of benzenoid ring.The PL spectra of 0, 2, 4, 6 and 8 wt%

CuO doped PAni samples show peaks in visible emission peaks which at

around 362 nm, 405 nm in violet region 459 nm, 486 nm in blue region

and 528 nm in green region.

81

Chapter 4

Synthesis and Characterization of Undoped and Al2O3

Doped Polypyrrole Nanocomposites

4.1 Introduction

Conducting polymers (CPs) such as polythiophene (PTh), polyaniline

(PAni) and polypyrrole (PPy) however, arouse an immense interest

among researchers because of their curious electronic, magnetic and

optical properties [1-5]. Among the CPs, Polypyrrole (PPy) is one of the

most investigated polymers due to their environmental stability, relative

ease of synthesis, good electro-optical and mechanical properties [6].

Potential technological applications such as in electronic and

electrochromic devices, sensors, counter electrode in electronic

capacitors, chromatographic stationary phases, light-weight batteries, and

membrane separation consequently, have attracted great deal of attentions

recently [7-16]. Long term stability of PPy is a key factorfor application

of new polymeric material in future applicationsand seems to be a good

candidate [17]. Polymer-metal composites are attracting considerable

attention of the researchers due to their striking advantageous properties

such as easy processing flexibility and light weight [18-22]. Polypyrrole

is one of the most stable conducting polymers and also one of the easiest

to synthesize. It displays a good conductivity in combination with high

stability in its oxidized form. A polypyrrole that is polymerized

electrochemically or chemically is known to be insoluble.

Electrochemically polymerization on a metal electrode results in good

quality films [23], while chemical polymerization yields fine conducting

powders [24]. PPy is most frequently used in commercial application

such as batteries, super capacitors, sensors and corrosion protection.

Polymer–inorganic nano particle hybrids have attracted great

82

attention, since they have interesting physical properties and potential

applications [25]. Electronically conducting polymers have been great

interest to chemist and physicists in recent years because of large number

of possible applications of these materials in various electronic devices

such as electrochromic displays (ECD), light emitting diodes (LEDs),

field effect transistors (FETs), chemical sensors etc. [26]. Among those

conducting polymers, polypyrrole (PPy) is especially promising for

commercial applications because of its good environ-mental stability,

facile synthesis and higher conductivity than many other conducting

polymers. PPy can often be used as biosensors, gas sensors wires, micro

actuators, anti-electrostatic coatings, solid electrolytic capacitor,

electrochromic windows and displays, and packaging, polymeric

batteries, electronic devices and functional membranes, etc [27-35].

Aluminium oxide is a chemical compound of aluminium and oxygen with

the chemical formula Al2O3. It is also called alumina.It has a wide band-

gap of ~8.8 eV for bulk material.It is an electrical insulator but has a

relatively high thermal conductivity around 30 Wm−1

K−1

for a ceramic

material.Aluminium oxide is insoluble in water.Al2O3 has been

extensively investigated dopants to serve as catalysts, fire redundant,

absorbents and fillers for structural materials [36]. It is stable in acidic

and oxidative mediums and well known for reactivity with aromatic

organic materials.

Several methods have been used in the preparation of polypyrrole (PPy)

and a wide range of its derivatives by simple chemical or electrochemical

methods [13-16, 37-39]. In the present chapter, chemical polymerization

method is used in the preparation of PPy. It is a simple and fast process

with no need for special instruments. Bulk quantities of polypyrrole (PPy)

can be obtained as fine powders using oxidative polymerization of the

monomer by chemical oxidants in aqueous or non-aqueous solvents [15-

83

16, 37, 40] or by chemical vapour deposition [38]. However, the use of

chemical polymerization limits the range of conducting polymers that can

be produced since only a limited number of counterions can be

incorporated. The chemical polymerization of Pyrrole appears to be a

general and useful tool for the preparation of conductive composites

[41,42] and dispersed particles in aqueous media [43, 44].

4.2 Experimental

4.2.1 Synthesis of Polypyrrole

The polypyrrole was prepared by chemical polymerization method. In

this approach, 1M pyrrole solution was prepared using distillation and

then mixed with an oxidizing agent ammonium persulphate slowly added

under constant stirring for 30 minutes. Then the polymerization was

conducted for 4 hours under constant stirring. This preparation was kept

un-agitated for 24 hours so that polypyrrole powder settled down. The

polypyrrole powder was filtered out and washed with distilled water

several times to remove any impurities present in the samples. The

synthesized polypyrrole has been doped by Al2O3 in ratio of 2, 4 and 6

wt%. The undoped and doped polypyrrole was ground in form of fine

powder. Pellets were prepared by compressing the powder under a

pressure of 10 tons with the help of a hydraulic press machine. All the

pellets are annealed at 1000C for 1hour. The diameter of the pellets was

found to be 13 mm. The 0, 2, 4 and 6wt% Al2O3 doped polypyrrole

samples was denoted as samples a, b, c, and d respectively.

4.2.2 Characterizations

The XRD spectra of all the samples recorded by Phillips X’pert PW3020

diffractometer using CuKα radiation (λ=1.54056 Ao) were presented for

structural analysis of the samples. The SEM images of all the pellets were

taken by scanning electron microscope (Model-430, LEO Cambridge,

84

England). FTIR spectra of all the samples in the form of powder were

recorded on the Bruker Alpha spectrometer to determine the formation of

polythiophene. To record absorbance spectra, 0.01 gm of each sample is

dissolved in 5 ml of dimethyl formamide (DMF). Then the absorption

spectra of the solutions thus formed were recorded with UV-vis

spectrophotometer (Model No.V-670 Jasco). PL spectra of all the

samples were recorded using LS-55, Perkin Elmer fluorescence

spectrometer at room temperature with excitation wavelength (λexc.) 325

nm.

4.3 Results and discussion

4.3.1 X-Ray Diffraction (XRD)

XRD spectra of undoped PPy and PPy/Al2O3 nanocomposites are shown

in Fig. 4.1. Undoped sample shows only one broad peak at 260 which

shows poor crystallinity phase of PPy (curve a) and corresponds to (101)

plane. Samples b, c and d shows two main peaks one at 25.850 and other

at 30.890 which corresponding to (101), (004) plane of PPy/Al2O3

nanocomposites. XRD patterns of PPy/Al2O3 nanocomposites show that

the broad weak diffraction peak of PPy still exists, but its intensity has

been decreased. It implies that when pyrrole is polymerized on Al2O3,

each phase maintains his initial structure [45-46].The crystallite size, D,

is calculated for undoped PPy and PPy/Al2O3 nanocomposites using

relation [47]:

D = kλ/β cosθ,

where, λ, is the X-ray wavelength; k, the shape factor; D, the average

diameter of the crystals in angstroms; θ, the Bragg angle in degree; and β

is the line broadening measured by half-height in radian. The value of k

depends on several factors including the miller index of the reflection

plane and the shape of crystal. If the shape is unknown, k is often

85

considered to be 0.89. The crystallite sizes of PPy/Al2O3 nano-composites

are formed to lies between 10 nm to 20 nm.

4.3.2 Scanning Electron Microscopy (SEM)

Scanning electron microscopy (SEM) is used here to study the surface

morphology of the samples. SEM images of the samples show the

formation of spongy structures (Fig.4.2), which are almost the same for

undoped and PPy/Al2O3 nanocomposite samples. Figure 4.2(a–d)

corresponds to 0, 2, 4 and 6 wt% PPy/Al2O3 nanocomposites

respectively. The spongy structure formation in the polypyrrole takes

place by heterogeneous nucleation. As a result granular coral like

structures are formed. As a characteristic of polypyrrole, secondary

nucleation also takes place because of which the granular coral like

particles come together to form aggregates. We noticed that as the

amount of Al2O3 is increased, the number of pores and the size of pores

are also increased, which is very important parameter for sensing

properties. Small change in the morphology has been observed in SEM

images after doping. The change in morphology can be explained by the

adsorption and intercalation of PPy on the surface of Al2O3. There is

another possibility that the Al2O3 is sandwiched between the PPy layers

or Al2O3 uniformly mixed into the PPy matrix. The pyrrole monomer is

likely to be absorbed onto the surface of Al2O3 through electrostatic

attraction and by the formation of weak charge-transfer complexes

between pyrrole monomer and the structure of Al2O3. As a result of this

absorption process Al2O3 are finely coated by PPy particles by the

polymerization of pyrrole monomer. Thus, it is appropriately believed

that adsorption probability of pyrrole monomer on the whole surface of

Al2O3 is equipotent, resulting in the formation of continuous PPy coating

on the surface of Al2O3. Therefore, because of the change in surface

morphology, porosity of the PPy increases with the addition of the Al2O3.

86

Fig. 4.1: XRD spectra of the samples a, b, c and d i.e.0, 2, 4 and 6 wt%

doping of Al2O3 in PPy Curves a, b, c and d correspond to samples a, b ,c

and d respectively.

87

Fig. 4.2: SEM images of the samples a, b, c and d i.e. 0, 2, 4 and 6 wt%

doping of Al2O3 in PPy/Al2O3 nanocomposites. Curves a, b, c and d

correspond to samples a, b, c and d respectively.

88

4.3.3 Optical Properties

Fourier Transform Infrared (FTIR) Spectroscopy

Fourier transforms infrared (FTIR) spectra of all the samples are obtained

in the range 500–4000 cm-1

and are shown in Fig. 4.3. The peak around at

936cm-1

is observed in all samples that are because of N–H out-of-plane

bending [48]. The C–N stretching vibrations mode in the polymer chain

gives rise to peak at 1109 cm-1

. The peak around at1400cm-1

may be

attributed to the in-plane deformation of the N–H bonds. The peaks

around at1580 cm-1

may be attributed to N-H bending vibration [49-50].

The absorption peaks are present in all the samples from (a – d) and no

significant shift is observed in any of the samples.

UV-visible absorption spectroscopy

The UV-visible absorption spectra of the polypyrrole and the PPy/Al2O3

nanocomposites are recorded at room temperature by using a

spectrophotometer between the wavelength range 275-650 nm and are

shown in Fig. 4.4. The UV-vis absorption can significantly determine the

interaction between the Al2O3 and PPy. Solutions of all the samples show

peak at 306 nm. The peak at 306 nm is associated with the exciton

transition of π–π* [51-54]. Intensity of the peak is randomly varied as the

dopant concentration increased and there is no shift in the peak at 306

nm.

89

Fig.4.3: FT-IR spectra of the samples a, b, c and d i.e. 0, 2, 4 and 6 wt%

doping of Al2O3 in PPy/Al2O3 nanocomposite. Curves a, b, c and d

correspond to samples a, b, c and d respectively.

90

Fig. 4.4: UV-vis absorption spectra of the samples a, b, c and d i.e. 0, 2, 4

and 6 wt% doping of Al2O3 in PPy/Al2O3 nanocomposites. Curves a, b, c

and d correspond to samples a, b, c and d respectively.

91

Photoluminescence (PL) spectroscopy

The photoluminescence (PL) properties of the polypyrrole/Al2O3

nanocomposites are studied using LS-55, Perkin Elmer fluorescence

spectrometer at room temperature with excitation wavelength (λexc.)

325nm. Fig.4.5 shows the main emission band of the nanocomposites is

located at 365 nm with two shoulders at 473 nm and 533 nm. The

observed reduced height of the photoluminescence emission intensity

peaks with increased wt% Al2O3 doped PPy might due to the possibility

of atoms/molecules of dopant (Al2O3) forming aggregation in the polymer

chains [55-57].The direct band gap is calculated by using this formula,

(Eg= hc/λ) where, ‘h’ is a constant, ‘c’ is velocity of light, ‘λ' is emission

wavelength in photoluminescence spectrum. The direct band gap energies

of the PPy/Al2O3 composite of different ratios are found as 3.09 and 2.19

eV. The band gap gets decreased due to increased content of Al2O3

nanoparticles. As the luminescence of these oxide/polymer

nanocomposites is proportional to the surface features, it is possible to

tailor the wavelength and the intensity of the luminescence by varying the

particle size.

92

250 300 350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

Inte

ns

ity

(a

.u.)

Wavelength (nm)

Pure PPy

PPy: 2wt% Al2O3

PPy: 4wt% Al2O3

PPy: 6wt% Al2O3

Fig. 4.5: Photoluminescence of the samples a, b, c and d i.e. 0, 2, 4 and 6

wt% doping of Al2O3 in PPy/Al2O3 nanocomposites. Curves a, b, c and d

correspond to samples a, b, c and d respectively.

93

4.4 Conclusion

In this chapter, we have synthesised undoped and Al2O3 doped PPy

samples by the chemical oxidation method. The prepared samples have

been characterized by XRD, SEM, FTIR, UV-Vis absorption and PL

spectroscopy. X-ray diffraction patterns of PPy/Al2O3 nanocomposites

result show several broad peaks while undoped sample shows only one

single peak indicating poor crystalline phase of PPy. In the SEM images,

the results were found granular coral like structures. As a characteristic of

Polypyrrole, secondary nucleation also takes place because of which the

granular coral like particles come together to form aggregates. We

noticed that as the amount of Al2O3 was increased; the number of pores

and the size of pores were also increased, which is very important for

sensing. The study of FTIR spectra confirms the formation of PPY and

also suggests that doping of Al2O3 in PPY does not affect its structure.

The UV absorption can significantly determine the interaction between

the Al2O3 and PPy. Solutions of all the samples show peak, which

oriented around 306 nm. The peak at 306 nm is associated with the

exciton transition of π–π*. PL shows the main emission band of the

nanocomposites is located at 365 nm with two shoulders at 473 nm and

533 nm. The direct band gap energies of the PPy/Al2O3 nanocomposite of

different ratios are found as 3.09 and 2.19 eV. The band gap gets

decreased due to increased content of Al2O3 nanoparticles.

94

Chapter 5

Structural, Morphological and Optical Studies of Undoped

and Al2O3 Doped Polyaniline Thin Films

5.1 Introduction

Polyaniline is most attractive conducting polymer because of its low cost,

high environmental stability, good electrical conductivity and potential

applications in molecular electronics [1]. The electrical properties of

polymers can be modified by addition of inorganic fillers. Nanoscale

particles are more attractive due to intringuing properties arising from the

nanosize and large surface area [2-3]. Polyaniline is one of the most

studied conducting polymers known to date because of it is relatively

cheap, easy to synthesise and very stable under a wide variety of

experimental conditions. Like other classes of conducting polymers,

polyaniline is also easy to handle and can be readily processed into

polymeric blends [4]. Intrinsically conducting polymer thin films have

been used in various kinds of electronic devices [5-8]. Conducting

polymers are combined with metal oxides because of their enhanced

physical and electronic properties and find useful applications in various

devices such as sensors, electrodes, batteries and photovoltaics [9-14].

Polymer metal composites are attracting considerable attention of the

researchers due to their striking advantageous properties such as easy

processing flexibility and light weight [15-17]. However it is still difficult

to fabricate PAni with different nanostructures through a simple chemical

process. Polymer–metal composites are the potential candidates for the

researchers and scientific communities due to their remarkable

advantageous properties such as easy processing and light weight etc.

[18–22]. All conducting polymers exhibit reversible redox behavior with

95

a distinguished chemical memory and hence have been considered as a

most important class of new materials for the fabrication of biological

and chemical sensors. The adsorption and desorption of volatile species

cause a measurable change in the resistance of conducting polymers.

Conducting polymeric sensors have advantages over metal oxide sensors.

First a wide variety of polymers are available. Secondly, they are easily

grown by chemical polymerization of monomer and also sense at room

temperature [23–25]. Among the conducting polymers, polyaniline

(PAni) is advantageous because of comparatively high conductivity that

can be achieved by doping [25-28]. Fabrication of PAni with different

nanostructures without using any foreign material is difficult.

Conducting polymers such as polyaniline, polypyrrole, polythiophene etc,

have attracted considerable attention for their unique properties and their

potential application in a number of growing technologies. Their

supremacy is demonstrated by wide range of dependent applications such

as electrodes for batteries, energy storage, electrochemical display

devices, electromagnetic interference (EMI) shielding [29], corrosion

protection [30], organic light emitting diodes, plastic solar cells,

optoelectronic devices [31 ] etc. Most of the above applications are based

on thin film technology. In case of conducting polymers, such films can

be easily prepared by chemical/electrochemical polymerisation or by

solution processing techniques [34-36]. In the chemical polymerization

process, monomers are oxidized by oxidizing agents or catalysts to

prepare conducting polymers. The advantage of chemical synthesis is that

it offers mass production at reasonable cost. On the other hand

electrochemical method involves the direct formation of conducting

polymers with better control of polymer film thickness, internal

morphology and minimizing the contamination due to oxidant residues

[32-33,37-39]. Solution processing techniques such as spin coating are

96

used to prepare thin films of those polymers which are soluble in a

solvent or mixture of solvents. In spin coating process, film thickness and

morphology is controlled by spin rate and time of rotation, which make

them suitable for use in sensing, electro chromic and other electronic

applications.

Aluminium oxide is a chemical compound of aluminium and oxygen with

the chemical formula Al2O3. It is also called alumina.It has a wide band

gap of ~8.8 eV for bulk material.It is an electrical insulator but has a

relatively high thermal conductivity around 30 Wm−1

K−1

for a ceramic

material. Aluminium oxide is insoluble in water.Al2O3 has been

extensively investigated dopants to serve as catalysts, fire redundant,

absorbents and fillers for structural materials [40]. It is stable in acidic

and oxidative mediums and well known for reactivity with aromatic

organic materials. The use of inorganic component such as Al2O3 can

assist the process. It can serve as a catalyst, absorbent, fire retardant, as

well as filler for structural materials. In addition, Al2O3 is stable in both

acidic and oxidative environments during polymerization of aniline. Thus

Al2O3 is a good candidate as seed to fabricate different PAni/Al2O3

nanostructures. Several device applications of PAni include electrodes of

rechargeable batteries, sensors, electrochromic displays, and photovoltaic

devices [28].

5.2 Experimental

5.2.1 Synthesis of Polyaniline

Aniline hydrochloride (2.59 g) was dissolved in distilled water in a

volumetric flask to make 50 mL solution. Ammonium peroxydisulfate

(5.71 g) was dissolved in water of 50 mL of solution. Both the solutions

were kept for 1 hour at room temperature. They were then mixed with a

brief stirring and left at rest to polymerization. The solution turned to

97

dark green within few minutes. Now, we were prepared precursor

solutions for undoped PAni and PAni doped with Al2O3 as 2, 4, 6 and 8

wt %. The films were prepared on glass substrate by dip coating method

for all solutions. We take all the solutions in different beakers of 200 ml

and dipped one glass slide in each solution and rest it for 24 hours for the

deposition of thin films. After deposition of thin films on the glass slide,

we removed it from the solution one by one and washed several times

with 100 ml portions of 0.2 M HCl to remove the unreacted aniline and

its oligomers from the precipitate. After this process, thin films were

washed again several times with 100 ml portions of acetone to absorb the

water molecules and for the removal of any residual organic impurities.

Finally all thin films are annealed at 100 oC in furnace. The 0, 2, 4, 6 and

8 wt% Al2O3 doped PAni thin films are denoted as samples a, b, c, d and

e respectively.

5.2.2 Characterizations

The XRD spectra of all the sample of thin films recorded by Phillips

X’pert PW3020 diffractometer using CuKα radiation (λ=1.54056 Ao)

were presented for structural analysis of the samples. The SEM images of

all the thin films were taken by scanning electron microscope (Model-

430, LEO Cambridge, England). FTIR spectra of all the samples in the

form of thin films were recorded on the Bruker Alpha spectrometer to

determine the formation of PAni. The absorption spectra of the thin films

were recorded with UV-vis spectrophotometer (Model No.V-670 Jasco).

PL spectra of all the samples were recorded using LS-55, Perkin Elmer

fluorescence spectrometer at room temperature with excitation

wavelength (λexc.) 325nm.

98

5.3 Results and discussion

5.3.1 X-ray diffraction (XRD)

XRD spectra of the undoped and Al2O3 doped PAni samples a, b, c, d and

e (Fig. 5.1) show weak crystalline quality of all the samples. There is a

main peak around 2θ =24.39o

in sample a, b, c and around 24.55o in

samples d and e, which correspond to (110) plane. The same peaks of

PAni are earlier reported by Zhu et al. and Krishna et al [41, 42]. There is

no peak for the aluminium oxide in the composite sample or other

impurities level. In addition, the new peak at 2θ = 55.08o

in 8 wt% Al2O3

doped sample is found to have appeared that shows the higher doping

percentage of Al2O3, affects the lattice structure of PAni. The XRD

spectra suggest that during the doping of metal-oxides in PAni, it

undergoes interfacial interactions with metal crystallites and losses its

own morphology. The particle size for all the samples is estimated from

Debye–Scherrer’s (DS) formula:

cos

ktDS

where tDS is the crystallite size, λ is the wavelength of radiation used, θ is

the Bragg’s angle and β is the full-width at half-maximum (FWHM)

measured in radian. The calculated average crystallite size of all the

samples lies in the range between 30 to 55 nm.

99

Fig. 5.1: X-ray diffraction (XRD) spectra of the samples a, b, c, d and e

i.e. 0, 2, 4, 6 and 8 wt% doping of Al2O3 in PAni thin films. Curves a, b,

c, d and e correspond to a, b, c, d and e respectively.

100

5.3.2 Scanning Electron Microscopy (SEM)

Scanning electron microscopy (SEM) is used here to study the surface

morphology of the samples. SEM images of the samples show the

formation of spongy shaped spherical structures. In Fig. 5.2, samples a, b,

c, d and e correspond to 0, 2, 4, 6 and 8 wt% Al2O3 doped PAni

nanocomposites thin films respectively. The spongy structure formation

in the polyaniline takes place by heterogeneous nucleation. As a result,

granular coral like structures are formed. As a characteristic of

polyaniline, secondary nucleation also takes place because of which the

granular coral like particles come together to form aggregates. We have

noticed that as amount of Al2O3 is increased, the granular coral like

structures changes into spongy shaped spherical structures which are

clearly evidenced in 8 wt% Al2O3 doped PAni sample. The change in

morphology can be explained by the adsorption and intercalation of PAni

on the surface of Al2O3. There is another possibility that the Al2O3 is

sandwiched between the PAni layers or Al2O3 uniformly doped into the

PAni matrix as reported in literature [43]. The aniline monomer is likely

to be absorbed onto the surface of Al2O3 through electrostatic attraction

and by the formation of weak charge-transfer complexes between aniline

monomer and the structure of Al2O3. As a result of this absorption

process, Al2O3 are finely coated by PAni particles by the polymerization

of aniline monomer [43].

101

Fig. 5.2: SEM images of the samples a, b, c, d and e i.e. 0, 2, 4, 6 and 8

wt% doping of Al2O3 in PAni thin films. Curves a, b, c, d and e

correspond to samples a, b, c, d and e respectively.

102

5.3.3 Optical properties

Fourier transform infrared (FTIR) Studies

Fourier transform infra-red (FTIR) spectra of undoped PAni and

PAni/Al2O3 thin film samples are recorded in the transmission range 400

to 4000 cm-1

are shown in Fig. 5.3. In a spectrum the band observed at

3739 cm-1

is due to N-H stretching. The polymer shows the broad peak at

2346 cm-1

is associated with NH + unsaturated amine [43-45]. The

absorption peaks observed at 1698 cm-1

is attributed to C=C stretching in

aromatic nuclei. The bands obtained at 1600-1500 cm-1

corresponds to C-

H stretching in aromatic compounds [46]. The absorption peaks at around

1525 cm-1

is assigned to the quinoide ring structure of PAni [47]. FTIR

spectra of all the samples show strong absorption band in the region 750-

1500 cm-1

, which correspond to the characteristics of PAni. The

absorption bands lies below 1000 cm-1

are the characteristics of mono

substituted benzene [48,49].The out-of-plane bending of C–H in the

substituted benzene ring is reflected in the 867 cm-1

peak. These results

are in good agreement with the previous spectroscopic characterization of

polyaniline [50,51]. Therefore, it can be concluded that PAni co-exists

with inorganic Al2O3 in the PAni/Al2O3 thin films on the basis of the

FTIR spectral similarity between the PAni/Al2O3 thin films and the

undoped PAni thin film as well as the FTIR spectral features of Al2O3.

103

Fig. 5.3: FTIR transmission spectra of the samples a, b, c, d and e i.e. 0,

2, 4, 6 and 8 wt% doping of Al2O3 in PAni thin films. Curves a, b, c, d

and e correspond to samples a, b, c, d and e respectively.

104

UV-visible absorption spectroscopy

The UV-visible absorption spectra of undoped PAni and PAni/Al2O3 thin

film samples are recorded at room temperature by using a

spectrophotometer between the wavelength range 200-900 nm and are

shown in Fig. 5.4. The UV absorption spectra have been recorded with

base line. The UV absorption can significantly determine the

interaction between the Al2O3 and PAni [52]. All the samples show

single broad peak at around 305 nm and small peak at around 450 nm.

The peak 305nm is associated with the exciton transition of π-π*. The

longer wavelength peak at around 450 nm can be associated to the

transition between benzenoid to quinoid rings [55]. Intensity of the peak

is randomly varied as the dopant concentration increases [54]. Normally,

the change in first peak is because of the degree of oxidization and the

change in other peak is because of the change in polymerization [53,55-

56].

Photoluminescence (PL) spectroscopy

Most of the electronic polymers exhibit photoluminescence (PL) only in

their reduced state. Much like other polymers, PAni also exhibits visible

emission in the solid state and in the solution. In the present work, the

photoluminescence studies of undoped PAni and Al2O3 doped PAni thin

films have been carried out with excitation wavelength of 325 nm and are

given in Fig. 5.5. The PL spectra show a strong peak in UV region at

around 384 nm and several weak visible emission peaks located at around

450 nm in blue region, 484 nm in blue-green and 525 nm in green

emission region. The peak in UV region is reported in literature [57]. The

overall intensity of UV region peak in doped samples is found to decrease

as compared to undoped sample. The intensity decreases for sample b, c,

with respect to undoped sample a, it again increases PL intensity for

105

sample d and e samples. The visible emission peaks don’t show any

significant changes in the intensity of PL. The decrease in intensities of

PL with the increase of dopant concentration in PAni indicates the change

in the oxidation state of the doped PAni. It has been reported that PAni

exhibits visible emission in the half oxidized state under solid state [1].

The relative heights of the emission peaks alter with different dopant

concentrations and nature of solvents may be due to polarity. In addition,

this peak becomes sharp and intense. This may be due to interchain

species which plays an important role in the emission process of

conjugated polymers. The intensity of peaks depends on factors such as

polymer coil size, the nature of polymer-solvent, polymer-dopant

interactions, and the degree of chain overlapping [58]. The PL spectra of

samples have the same shape, which indicates that it is an efficient way to

tune the intensities of the peak by employing specific dopant with

different wt%. The observed reduced height of the photoluminescence

emission intensity peaks with increased wt% Al2O3 doped PAni might

due to the possibility of atoms/molecules of dopant forming aggregation

in the polymer chain [59-60].

106

Fig. 5.4: UV-visible absorption spectra of the samples a, b, c, d and e i.e.

0, 2, 4, 6 and 8 wt% doping of Al2O3 in PAni thin films. Curves a, b, c, d

and e correspond to samples a, b, c, d and e respectively.

107

Fig. 5.5: Photoluminescence (PL) spectra of the samples a, b, c, d and e

i.e. 0, 2, 4, 6 and 8 wt% doping of Al2O3 in PAni thin films. Curves a, b,

c, d and e correspond to samples a, b, c, d and e respectively.

108

5.4 Conclusion

In this chapter, we have synthesized undoped and Al2O3 doped PAni thin

films by the chemical oxidation method. The prepared thin films have

been characterized by XRD, SEM,UV-vis, FTIR and PL. The XRD

spectra shows a peak around 25o which confirm the synthesis of PAni and

another peak at 55.08o

for 8 wt% Al2O3 doped PAni which is

confirmations of successful doping in PAni. The study of FTIR spectra

again confirms the formation of PAni. SEM images show the granular

coral like structure which converted into spherical shaped structures for

higher doping percentage. UV spectra show single broad peak at around

305 nm and small peak at around 450 nm. The peak 305nm is associated

with the exciton transition of π-π*. The longer wavelength peak at around

450 nm can be associated to the transition between benzenoid to quinoid

rings. PL spectra recorded with excitation wavelength 325 nm show a

strong UV peak at 384 nm with weak visible peak at 484 nm and 527 nm.

109

Chapter-6

Structural, Morphological and Optical Studies of Undoped

and TiO2 Doped Polypyrrole Thin Films

6.1 Introduction

Polypyrrole is one of the most stable conducting polymers and also one of

the easiest to synthesize. It displays a good conductivity in combination

with high stability in its oxidized form. Electrochemically polymerization

on a metal electrode results in good quality film [1]. In recent years,

electro-active polymers, particularly aromatic conducting polymers, have

received much research attention for use as advance materials due to their

remarkable physical attributes [2–4]. Conducting polymers (CP),

however, arouse an immense interest among researchers because of their

curious electronic, magnetic and optical properties. Conducting polymers

can be prepared by chemical or electrochemical polymerization. In the

chemical polymerization process, monomers are oxidized by oxidizing

agents or catalysts to produce conducting polymers. The advantage of

chemical synthesis is that it offers mass production at reasonable cost. On

the other hand, the electrochemical method involves the direct formation

of conducting polymers with better control of polymer film thickness and

morphology, which makes them suitable for use in electronic devices [5-

6]. Therefore, the physical and chemical properties of conducting

polymers are considerably dependent upon the dopant and polymerization

conditions. In terms of CP, Polypyrrole (PPy) is one of the most studied

polymers due to its environmental stability, relative ease of synthesis and

good electrical conductivity. Long term stability of PPy is a key factor for

application of new polymeric material in future applications and seems to

be a good candidate [7]. PPy is most frequently used in commercial

application such as batteries, super capacitors, sensors and corrosion

110

protection. Polymer–inorganic nano-particle hybrids have attracted great

attention, since they have interesting physical properties and potential

applications. These particles not only combine the advantageous

properties of metals and polymers but also exhibit many new characters

that single phase materials do not have [8]. The incorporation of the

conducting polymer as the shell in the core–shell structure can increase

the surface area of the conducting polymers over that of the bulk

polymer. This structure can be obtained from an in-situ chemical

oxidative polymerization in the presence of nanoparticles [9]. The

inorganic core can be a metal or a metal oxide, and the organic shell can

be a conducting polymer. Moreover, recent investigations on PPy/TiO2

nanocomposites (NCs) for use as pigments indicate that a TiO2

nanoparticle (NP) core can increase the charge resistance of the coatings

[10-12].

Titanium dioxide also known as titanium (IV) oxide or titania, is the

naturally occurring oxide of titanium, chemical formula TiO2.It has a

wide band gap of ˜ 3.2 eV.Generally it is sourced from ilmenite,

rutile and anatase. It has a wide range of applications, from paint

to sunscreen to food colouring. When used as a food colouring. The most

important application areas are paints and varnishes as well as paper and

plastics, which account for about 80% of the world's titanium dioxide

consumption. Other pigment applications such as printing inks, fibers,

rubber, cosmetic products and foodstuffs account for another 8%. The

rest is used in other applications, for instance the production of technical

pure titanium, glass and glass ceramics, electrical ceramics, catalysts,

electric conductors and chemical intermediates. It also used in most red-

coloured candy.

111

Titanium dioxide is the most widely used white pigment because of its

brightness and very high refractive index, in which it is surpassed only by

a few other materials. Approximately 4.6 million tons of pigmentary

TiO2 are used annually worldwide, and this number is expected to

increase as utilization continues to rise. When deposited as a thin films,

its refractive index and colour make it an excellent reflective optical

coating for dielectric mirrors and some gemstones like mystic fire topaz .

In paint application, it is often referred to offhandedly as the perfect

white, the whitest white, or other similar terms. Opacity is improved by

optimal sizing of the titanium dioxide particles. Some grades of titanium

based pigments as used in sparkly paints, plastics, finishes

and pearlescent cosmetics are man-made pigments whose particles have

two or more layers of various oxides–often titanium dioxide, iron

oxide or alumina in order to have glittering, iridescent and or pearlescent

effects similar to crushed mica or guanine-based products. In addition to

these effects a limited colour change is possible in certain formulations

depending on how and at which angle the finished product is illuminated

and the thickness of the oxide layer in the pigment particle; one or more

colours appear by reflection while the other tones appear due to

interference of the transparent titanium dioxide layers [13].

In some

products, the layer of titanium dioxide is grown in conjunction with iron

oxide by calcination of titanium salts (sulfates, chlorates) around 800 °C

[14] or other industrial deposition methods such as chemical vapour

deposition on substrates such as mica platelets or even silicon dioxide

crystal platelets of no more than 50 µm in diameter. The iridescent effect

in these titanium oxide particles (which are only partly natural) is unlike

the opaque effect obtained with usual ground titanium oxide pigment

obtained by mining, in which case only a certain diameter of the particle

is considered and the effect is due only to scattering. In ceramic

112

glazes titanium dioxide acts as an opacifier and seeds crystal formation.

Titanium dioxide has been shown statistically to increase skimmed milk's

whiteness, increasing skimmed milk's sensory acceptance score [15].

Titanium dioxide is used to mark the white lines of some tennis courts.

Several methods have been used in the preparation of polypyrrole (PPy)

and a wide range of its derivatives by simple chemical or electrochemical

methods [16-22]. In the present chapter, chemical polymerization method

is used in the preparation of PPy. It is a simple and fast process with no

need for special instruments. Bulk quantities of polypyrrole (PPy) can be

obtained as fine powders using oxidative polymerization of the monomer

by chemical oxidants in aqueous or non-aqueous solvents [18-23] or by

chemical vapor deposition [21]. However, the use of chemical

polymerization limits the range of conducting polymers that can be

produced since only a limited number of counter ions can be

incorporated. The chemical polymerization of pyrrole appears to be a

general and useful tool for the preparation of conductive composites

[24,25] and dispersed particles in aqueous media [26, 27].

6.2 Experimental

6.2.1 Sample preparation

The Polypyrrole was prepared by chemical polymerization method. 1 M

Pyrrole solution was prepared using distillation and then mixed with an

oxidizing agent ammonium persulfate slowly under constant stirring for

30 minutes. Then the polymerization was conducted for 4 hours under

constant stirring. This preparation was kept unagitated for 24 hours so

that polypyrrole powder settled down. The Polypyrrole powder was

filtered out and washed with distilled water several times to remove any

impurities present. The precursor solution has been prepared by

113

dissolving predetermined amount of polypyrrole in m-cresol. The mixture

is then magnetically stirred at 400C for half an hour to get a homogeneous

solution. To this solution appropriate weight of TiO2 is added in

polypyrrole solution to obtain TiO2 doping of 0, 10, 20, 30 and 40 wt.% .

All solutions are again stirred for 24 hours at same temperature. All the

solutions are aged for 15 days to achieve proper viscosity and stability.

The precursor solutions thus obtained are spin coated on glass slides.

Prior to film deposition the substrate of glass slides are properly cleaned

in an ultrasonic cleaner using methanol, acetone and de-ionized water.

Spinning speed is kept at 3000 rpm while the spinning time is 30 seconds.

The films thus obtained are dried at 1000C at the rate of 10

0 C/min for

two hours and then cooled back to room temperature. The process is

repeated twelve times to obtain appreciable thickness. After getting

appreciable thickness, the finally prepared the precursor films were

annealed at 1000C for 4 hours. The 0, 10, 20,30 and 40 wt% TiO2 doped

PPy thin films are denoted as samples a ,b ,c ,d and e respectively

6.2.2 Characterizations

The XRD spectra of all the samples recorded by PANalytical, X’pert

PRO diffractometer using CuKα radiation (λ=1.54056 Ao) were presented

for structural analysis of the samples. The SEM images of all the thin film

samples were taken by scanning electron microscope (Model-430, LEO

Cambridge, England). FTIR spectra of all the samples in the form of thin

films were recorded on the Bruker Alpha spectrometer to determine the

formation of polyaniline. The Photoluminescence (PL) spectra were

recorded for all samples in the form of thin films by Perkier Elmer

photoluminescence spectrophotometer (LS-55, Perkin Elmer fluorescence

spectrometer) at excitation (λexc) wavelength 325 nm. The incident

excitation density was controlled by using calibrated neutral density

114

filters in front of the spectrometer slit. The slit widths for emission

spectra recording have been chosen as 10nm. The excitation source was a

20 kW Xenon discharge lamp. The light beam used for excitation is

focused on the film surface in circular area of diameter ~5nm.

6.3 Results and discussion

6.3.1 Structural Analysis

Fig 6.1 shows the X-ray diffraction (XRD) patterns of undoped PPy and

TiO2 doped PPy thin films. The broad peak in the region of 2θ = 20–800

in XRD pattern of undoped PPy and TiO2 doped PPy films show weak

crystalline quality of all the samples. The XRD spectra show the

appearance of peaks at 24.66o, 29.39

o, 37.95

o, 42.47

o, 44.05

o, 47.19

o,

53.28o and 64.37

o match with JCPDS data No: 21-1276 [28] which

confirms the existence of PPy/TiO2. However, it is seen due to the PPy

deposition on the surface structure of TiO2 nanostructures, the diffractions

of TiO2 gets slightly shifted from their positions [29]. The crystallite

sizes of all the samples are calculated using Debye–Scherrer’s (DS)

formula [30]:

cos

ktDS ,

where tDS is the crystallite size, λ is the wavelength of radiation used, θ is

the Bragg’s angle and β is the full-width at half-maximum (FWHM)

measured in radian. The average crystallite size of all the samples lies in

the range between 30 to 50 nm.

115

6.3.2 Scanning Electron Microscopy (SEM)

Scanning electron microscope (SEM) is used to study the surface

morphology of the pure polypyrrole and polypyrrole doped with various

dopant percentages of TiO2 thin films as shown in Fig. 6.2(a-e), which

show the smooth surface morphology. SEM images shown in Fig.6.2 (b-

d) for the PPy/TiO2 thin films have large nanospheres are due to the

introduction of the relatively higher content of TiO2. The particle size of

all the samples is found in the range of 40-50 nm. It is seen that the

particle size decreases with increasing doping concentration as well as

number of pores and size of the pores also increases with dopant. The

increase of number of pores shows the suitable application in the sensing

properties. It is the initiator molecules act as a stabilizer for the as-formed

nano micelles. These nano micelles are acting as templates to encapsulate

pyrrole and oxidant leading to the formations of nanospheres during the

polymerization [28, 31].

.

116

Fig 6.1: XRD spectra for the samples a, b, c and d. Curves a, b, c and d

corresponds to 0, 10, 30 and 40 wt% TiO2 doped PPy thin films

respectively.

.

117

Fig 6.2: SEM images of samples a, b, c, d and e. Images a, b, c, d and e

are correspond to 0, 10, 20, 30 and 40 wt% TiO2 doped PPy thin films

respectively.

118

6.3.3 Optical properties

Fourier Transform Infrared (FTIR) Spectroscopy

The Fourier transform infrared (FTIR) transmittance spectra of undoped

PPy and TiO2 doped PPy thin films are recorded in the range of 600 -

4000 cm-1

, which is shown in Fig.6.3 (a-e). The FTIR spectra of undoped

PPy and TiO2 doped PPy thin films are found the different absorbance

band and it conform the synthesis and chemical structure of PPy. The

peaks at 739 cm-1

and 881 cm-1

can be attributed to C-H out-of-plane

vibrations [32]. The absorbance band observed in the range of 1400 cm−1

to 1600 cm−1

in the FTIR spectra of the synthesized polymers can be

attributed to the fundamental vibrations of the pyrrole rings [15]. The

absorbance band at 1690 cm-1

corresponds to C-N=C bond, the peaks at

3732 cm−1

and 3848 cm−1

are attributed to N–H bond [33-34]. The FTIR

spectrum of TiO2 doped PPy thin films in Fig.6.3 (b-e) are similar to the

undoped PPy spectrum, which shows that PPy chains have been formed

in the doped thin films. However, the incorporation of TiO2 leads to the

obvious small shift of some FTIR bands of PPy. TiO2 probably led to the

reduction of the conjugation length of PPy in TiO2 doped PPy thin films

[35-36].

119

Fig. 6.3 FTIR spectra for the sample a, b, c, d and e. Curves a, b, c, d and

e correspond to 0, 10, 20, 30 and 40 wt% TiO2 doped PPy thin films

respectively.

120

UV-visible absorption spectroscopy

The UV–vis absorption spectra of undoped PPy and TiO2 doped PPy thin

films are recorded at room temperature by using a spectrophotometer

between the wavelength range 300–1500 nm as shown in Fig. 6.4. Optical

spectroscopy is an important technique to understand the conducting

states corresponding to the absorption bands of inter and intra gap states

of conducting polymers [37].The thin films of undoped PPy and TiO2

doped PPy show the observed peak at 309 nm as seen in the Fig. 6.4

which may be due to the π-π* transition or the excitation transition [38].

As the dopant percentage of TiO2 increases, the intensity of TiO2 doped

ppy thin films increased and the polaron band appears to be sharp peak.

This indicates that an increase in the dopant percentage leads to the

formation of a chain which forms the best sharp peaks [39]. The

differences between the spectra are due to the presence of an electron-

withdrawing sulfonic group in the complex and therefore the transition

band is observed at a lower wavelength. The absorption of the polaron

band is strongly dependent on the molecular weight of the polymer [40].

121

Fig.6.4: UV–vis absorbance spectra for the sample a, b, c, d and e.

Curves a, b, c, d and e correspond to 0, 10, 20, 30 and 40 wt % TiO2 and

PPy/TiO2 thin films.

122

Photoluminescence (PL) Studies

Photoluminescent of organic materials have a new class with interesting

properties. They undergo emission over a wide range from the violet to

the red. They can also be combined in several different forms to produce

white light. One category of organic material with photoluminescence

properties is conjugated organic polymers. PL spectra were measured for

all the four samples in the range of 325-650 nm and the wavelength of

excitation chosen for all the samples is 325 nm. The photoluminescence

(PL) of TiO2 doped PAni has been performed and is shown in Fig. 6.5.

The PL spectra of 0, 10, 20, 30 and 40 wt% TiO2 doped PPy samples

show a broad peak in visible emission around at 385 nm. One of the

similar related peaks are reported for the PL spectra of TiO2 doped PPy

observed at the 362 nm [37]. The direct band gap was calculated by using

this formula,

(Eg= hc/λ)

Where ‘h’ is a constant ‘c’ is velocity of light, ‘λ’ is emission wavelength

in Photoluminescence spectrum. The direct band gap energies of undoped

PPy and TiO2 doped ppy thin films of different wt% are found to be the

corresponding main visible emission peaks as 3.65 eV. As the

luminescence of this oxide/polymer nanocomposite is proportional to the

surface features, it is possible to tailor the wavelength and the intensity of

the luminescence by varying the particle size [41, 42]. In addition, PL

spectra of all the samples show the small visible emission peaks located

at around 480 nm and 530 nm in green region. Similar peaks have been

observed in our earlier reported chapter 4.

123

Fig. 6.5: Photoluminescence spectra for the samples a, b, c, d and e.

Curves a, b, c, d and e correspond to 0, 10, 20, 30 and 40 wt% TiO2 and

PPy/TiO2 thin films respectively.

124

6.4 Conclusion

In the present chapter, we have synthesized undoped PPy and TiO2 doped

PPy nanocoposite thin films by the chemical oxidation method at room

temperature. The prepared samples have been characterized by XRD,

SEM,UV-vis, PL and FTIR. XRD spectra show the weak crystalline

quality of all the samples. SEM images show the sphere shape of

nanostructures. The amount of TiO2 doping increases the number of pores

as well as size of the pores that play a very important role in sensing of

gas. The study of FTIR spectra confirms the formation of conducting PPy

which suggests that doping of TiO2 in PPy does not affect its structures.

All the samples of PPy and PPy/TiO2 nanocomposites thin films show the

peak at 309 nm which is assigned to the π-π* transition or the excitation

transition. The PL spectra of PPy and TiO2 doped PPy show three main

peaks, first is in UV region around at 368 nm, second broad peak in

visible region around 480 nm and another sharp peak at around 530 nm in

green region.

125

Chapter 7

Conclusion

The present thesis is an effort to synthesize the polymer and poymer

nanocomposite for various important applications. Ploythiophene (PTh),

polyaniline (PAni) and polypyrrole (PPy) have been used as a host

materials in pellets and thin films form. The different metal oxide dopants

such as Al2O3, CuO and TiO2 have been used to improve the structural,

morphological and optical properties of synthesized samples. Sol-gel

spin coating, dip coating has been used to deposit the films for

present investigations. Undoped and Al2O3 doped polythiophene and

polypyrrole, undoped and CuO doped polyaniline pellets are also

prepared. The synthesized samples are characterized by various

characterizations techniques including XRD, SEM, FTIR, UV-vis and

PL. Thesis contains following chapters.

[1] introduction

[2] undoped and Al2O3 doped polythiophene pellets

[3] undoped and CuO doped polyaniline pellets

[4] undoped and Al2O3 doped polypyrrole pellets

[5] undoped and Al2O3 doped polyaniline sol-gel dip coating thin

films

[6] undoped and TiO2 doped polypyrrole sol-gel spin coating thin films

[1] Chapter 1 deals with the brief introduction of materials, their types

and applications. In this chapter, we have discussed about basics of

materials and three conducting polymers including polythiophene (PTh),

polyaniline (PAni) and polypyrrole (PPy) and their metal

126

nanocomposites. The metal dopants such as Al2O3, CuO and TiO2 have

been discussed in the present work. It also deals the discussion of

deposition techniques of the thin films as well as characterization

techniques. It also contains the organization and objective of thesis.

[2] in this chapter Undoped and Al2O3/polythiophene nanocomposites

have been synthesized by chemical oxidation method. The samples are

characterized by XRD, SEM, UV-vis, PL and FTIR spectroscopy. XRD

spectra show the polycrystalline nature of all the samples. SEM images

are indicating formation of spherical shape of nanostructures. As-

synthesized samples of undoped polythiophene and Al2O3/PTh

nanocomposites exhibit many pores on the surface of nanostructures.

Synthesis of Al2O3 polythiophene composite material is confirmed by

FTIR spectroscopy. UV-visible absorption spectra show absorption peak

at around 300 nm which is due to π- π* inter-band-transition of PTh

rings. A small change in optical absorption spectra is observed which can

be associated with the degree of oxidation. PL spectra exhibit mainly

three visible emission peaks at around 462 nm, 490 nm and 522 nm. The

two emission peaks 462 nm and 490 nm in the Soret band region where

as single peak at 522 nm in the Q band emission. The intensity and peak

position of polythiophene have been randomly changed with amount of

Al2O3 dopant.

[3] In this chapter, we have synthesized undoped and CuO doped PAni

nanocomposites by the chemical oxidation method at room temperature.

The prepared samples have been characterized by XRD, SEM, UV-vis,

PL and FTIR. XRD spectra show weak crystalline quality of all the

samples, whereas the PAni synthesized is amorphous in nature. The

scanning electron microscopy images of all the samples show granular

127

coral like structure. The study of FTIR spectra confirm the formation of

conducting PAni and also suggests that doped of CuO in PAni does not

affect the structures. The UV–visible absorption spectra of the solutions

of all the samples contain some peak at 300 nm.The observed

bathochromic shift at the intense absorption band 305nm is due to the π-

π* transition of benzenoid ring.The PL spectra of 0, 2, 4, 6 and 8 wt%

CuO doped PAni samples show in visible emission peaks which is at

around 362 nm, 405 nm in violet region 459 nm, 486 nm in blue region

and 528 nm in green region.

[4] In this chapter, we have synthesized undoped and Al2O3 doped PPy

nanocomposite samples by the chemical oxidation method. The prepared

samples have been characterized by XRD, SEM, FTIR, UV-Vis

absorption and PL spectroscopy. X-ray diffraction patterns of PPy/Al2O3

nanocomposites result show several broad peaks while undoped sample

shows only one single peak indicating poor crystalline phase of PPy. In

the SEM images, the results were found granular coral like structures. As

a characteristic of polypyrrole, secondary nucleation also takes place

because of which the granular coral like particles come together to form

aggregates. We noticed that as the amount of Al2O3 was increased; the

number of pores and the size of pores were also increased, which is very

important for sensing. The study of FTIR spectra confirms the formation

of PPY and also suggests that doping of Al2O3 in PPY does not affect its

structure. The UV absorption can significantly determine the interaction

between the Al2O3 and PPy. Solutions of all the samples show peak,

which oriented around 306 nm. The peak at 306 nm is associated with the

exciton transition of π–π*. PL shows the main emission band of the nano

composites is located at 365 nm with two shoulders at 473 nm and 533

nm. The direct band gap energies of the PPy/ Al2O3 nanocomposite of

128

different ratios are found as 3.09 and 2.19 eV. The band gap gets

decreased due to increased content of Al2O3 nano particles.

[5] In this chapter, we have synthesized undoped and Al2O3 doped PAni

thin films by the chemical oxidation method. The prepared thin films

have been characterized byXRD, SEM, UV-vis, PL and FTIR. The XRD

spectra shows a peak around 25o which confirm the synthesis of PAni and

another peak at 55.08o

for 8 wt% Al2O3 doped PAni which as the

confirmations of successful doping in PAni. The study of FTIR spectra

again confirms the formation of PAni. SEM images show the granular

coral like structure which converted into spherical shaped structures for

higher doping percentage. UV-vis spectra show single broad peak at

around 305 nm and small peak at around 450 nm. The peak 305 nm is

associated with the exciton transition of π-π*. The longer wavelength

peak at around 450 nm can be associated to the transition between

benzenoid to quinoid rings. PL spectra recorded with excitation

wavelength 325 nm show a strong UV peak at 384 nm with weak visible

peak at 484 and 527 nm.

[6] In this chapter, XRD spectra show the crystalline quality of all the

samples, whereas the PPy synthesized is amorphous in nature. The study

of FTIR spectra confirms the formation of conducting PPy and also

suggests that doping of TiO2 in PPy does not affect its structure. Optical

spectroscopy is an important technique to understand the conducting

states corresponding to the absorption bands of inter and intra gap states

of conducting polymers. Solution of all PPy and PPy/TiO2 sol-gel spin

coating films shows the observed peak at 308 nm was assigned to the π-

π* transition or the excitation transition. Pure PPy and PPy/TiO2 sol-gel

spin coating films as the dopant percentage of TiO2 increases, the

129

intensity of PPy/TiO2 sol-gel spin coating films increased and the polaron

band appears to be sharp peak. This indicates that an increase in the

dopant percentage leads to the formation of a chain which forms the best

sharp peaks. The PL spectra show one main peaks in visible emission

around at 384 nm and broad peak around 386 nm in blue region. SEM

images shows PPy/TiO2 have large nanospheres are due to the

introduction of the relatively higher content of TiO2. We noticed that as

the amount of TiO2 increased the number of pores and size of the pores

was also increased, which play very important role for conductivity.

In the chapter no.[2],[3] and [4], Al2O3 is doped in polythiophene (PTh)

and polypyrrole (PPy) while CuO is doped in polyaniline (PAni) in the

form of pellets. It is found that the crystallite size of PPy/Al2O3

nanocomposites is smaller than other two PTh/Al2O3 and PAni/CuO

nanocomposites. The porosity is found to increase significantly as

compared to other two nanocomposites of PTh/Al2O3 and PAni/CuO,

which can be very useful in gas sensing applications. PPy/Al2O3

nanocomposites exhibit larger PL intensity as compared to other two

nanocomposites of PTh/Al2O3 and PAni/CuO, which can be useful for

OLEDs.

In the last two Chapter [5] and Chapter [ 6], we have prepared thin films

using sol-gel dip coating and sol-gel spin coating thin films of Pani/

Al2O3 and PPy/TiO2 respectively. The overall structural, morphological

and optical properties of PAni/ Al2O3 thin films are found better as

compared to PPy/TiO2 thin films.

130

7.1 Recommendations for further work

a) Patterning of electrodes on sample pellets and films for further

observations.

b) Gas sensing and humidity sensing using above samples.

c) Study of effects of higher annealing duration and higher annealing

temperatures on structural, optical and the Gas sensing and humidity

sensitivity.

d) Further optimization of dopant concentration in Polymers like-

polypyrrole, polythiophene and polyaniline.

e) Study regarding selectivity and sensitivity to different gases like CO2,

LPG and NH3 etc..

131

References

Chapter 1

[1] Jr. Callister, Rethwisch, "Materials Science and Engineering–An

Introduction", John Wiley and Sons, 8th

ed. (2009) 5-12.

[2] R. D. Doherty et al., Materials Science and Engineering A, 238

(1997) 222.

[3] B. G. Yacobi, Semiconductor Materials: An Introduction to Basic

Principles, Springer, ISBN 0306473615, (2003) 1–3.

[4] M. Cutler and N. Mott, Physical Review, 181 (1969) 1336.

[5] J. W. Allen, Nature, 187 (1960) 403–405.

[6] T. Campbell, R. Kalia, A. Nakano, P. Vashishta, et al., Phy. Rev.

Lett., 82 (1999) 4866.

[7] J. B. Forsyth and S. Hull, J. Phys.: Condens. Matter, 3 (1991) 5257-

5261.

[8] J. V. Koleske, ASTM International, 232 (1995) ISBN: 978-0-8031-

2060-0.

[9] Phillips, G. Lance and Barbano, M. David, Journal of Dairy

Science, 80 (1997) 2726.

[10] Ye. P. Mamunya, et al., Eur. Polym. J., 38 (2002)1887-1897.

[11] R. Mülhaupt, Angew. Chem. Int. Ed., 43 (2004) 1054–1063.

[12] H. Shirakawa, et al. J. Chem. Soc. Chem. Commun.,13 (1977) 578-

580.

[13] C. K. Chiang, et al., Phys. Rev. Lett., 39 (1977) 1098–1101.

[14] C. K. Chiang, et al., J. Chem. Phys., 69 (1978) 5098-5104.

[15] C. K. Chiang, et al., J Am. Chem. Soc., 100 (1978) 1013–1015.

[16] T. Yasui, Bull. Chem. Soc. Japan, 10 (1935) 305-311.

132

[17] D. M. Mohilner, et al., J Electrochem. Soc, 84 (1962) 3618.

[18] R. de Surville, et al., Electrochim Acta, 13 (1968) 1451-1458.

[19] J. C. Chiang and A. G. MacDiarmid, Synth. Met., 13 (1986) 193-

205.

[20] B. A. Bolto, et al. Aust. J. Chem., 16 (1963) 1090–1103.

[21] M. G. Kanatzidis, Chem. Eng. News, 68 (1990) 36-54.

[22] K. E. Ziemelis, et al., Phys. Rev. Lett., 66 (1991) 2231-2234.

[23] A. F. Diaz, Chemica Scripta, 17 (1981)145–148.

[24] H. J. Ahonen, et al., Macromolecules, 33 (2000) 6787–6793.

[25] D. M. de Leeuw, et al., Synth. Met., 87 (1997) 53-59.

[26] J. H. Burroughes, et al., Nature, 335 (1988)137-14.

[27] J. H. Burroughes, et al., Nature, 347 (1990) 539-541.

[28] A. G. MacDiarmid, Synth. Met., 125 (2001) 11-22.

[29] A. J. Heeger, Physica Scripta, 102 (2002) 30-35.

[30] P. W. Anderson, Phys. Rev., 109 (1958) 1492–1505.

[31] W. L. McMillan, Phys. Rev. B, 24 (1981) 2739–2743.

[32] R. Menon, et al., 2nd

ed., Skotheim, Inc. New York, (1998) 27.

[33] R. S. Kohlman, et al., Phys. Rev. Lett., 74 (1995) 773–776.

[34] R. S. Kohlman, et al., Phys. Rev. Lett., 77 (1996) 2766–2769.

[35] A. Acharya, M. Rajkishore, Arm. J. of Phy. 3 (2010) 195-202

[36] "Trans IChemE, Part B, 85 (2007) 489–493".

[37] R. McNeill, R. Siudak, Aust. J. Chem.,16 (1963) 1056-75.

[38] H. Ray. Baughman, Science, 308 (2005) 63-65.

[39] J. Janata, M. Josowicz, Nature Materials, 2 (2003) 19-24.

[40] S. Geetha, R. K Chepuri. Rao, 568 (2006) 119–125.

[41] Unni, M Sreekuttan, J. Phy. Chem C, Vol (2010) 55047.

[42] S. T. Olson, J. Phys. Chem. C, 114 (2010) 5049.

[43] Okamoto, Yoshikuko and Brenner, Polymers, 23 (1964) 125–158.

133

[44] W. J. Feast, J. Tsibouklis, Polymer, 37 (1996) 5017.

[45] MacDiarmid, G Alan. Ang. Chem. Int. Edition, 40 (14) (2001)

2581.

[46] L.-M. Huang, Electrochimica Acta, 51 (2006) 5858.

[47] S. Virji, J. Huang, Nano Letters, 4 (2004) 491.

[48] Wessling, Bernhard, Polymers, 2 (2010) 786.

[49] S. Roy, S. Sana, B. Adhikari J. Poly. Mat., 20 (2003) 173-180.

[50] G. K. Prasad, Radhakrishnan, Sen. Actu. B, 106 (2005) 626-631.

[51] G. Korotcenkov, Com. Sen. Tech. Solid State Devices, 4 (2011).

[52] Ulrich, Roznyatovskaya, Analytica Chimica Acta, 614 (2008) 1–

26.

[53] A. F. Diaz, J. F. bargon, Conducting Polymers, New York, (1986)

81.

[54] J. D. Mackenzie and D. R. Ulrich, Sol-gel Optics, 1328 (1999) 2-

13.

[55] B. D. Fabes et al, 1328 (1990) 319-328.

[56] J. D. Mackenzie, Proc. of SPIE conf. on Sol-gel Optics, 878 (1988)

128.

[57] C.Y.Tsay,H.C.Cheng, C.Y.Chen, Thin Solid Films, 518

(2009)1603.

[58] Sao Carlos Ed. M. A.Aegerter, Utopia Press, Singapore (1989)1-

12.

[59] H. C. Cheng, C. F. Chen, C.Y.Tsay,Appl. Phys.Lett.,90 (2007)

012113.

[60] W. J. Park, H. S. Shin,Appl. Phys. Lett., 93 (2008) 083508.

[61] Y. Zhang, B. Lin, X. Sun, Appl. Phys. Lett., 86 (2005)131910.

[62] A. Jain, P. Sagar , Materials Science Poland, 25 (2007) 233.

134

[63] S-Y. Bae, C-S. Kim and Y-J. Oh, J. of Appl. Phys. 85 (8) (1999)

5226.

[64] G. Westin, M. Wijk , J. Sol-gel Sci. Tech., 31 (2004) 283.

[65] Y. Cao, L. Miao, Appl. Phys. Lett. 88 (2006) 251116.

[66] M. Paul1, A. Paliwa, Int. J. Elec. Ele. Eng., 7 (2014) 455-462.

135

Chapter 2

[1] M. Matsuguchi, J. Io, G. Sugiyama, Synthetic Metals, 128 (2002) 15–

19.

[2] R. Rella, P. Siciliano, F. Quaranta, Sen. Actu. B, 68 (2000) 203–209.

[3] M. K. Ram, O. Yavuz, M. Aldissi, Synthetic Metals, 151 (2005) 77–

84.

[4] S. Richard, P. Gnanakan, M. Rajasekhar Int. J. Electrochem. Sci., 4

(2009) 1289 – 1301.

[5] H. Meng, D. F. Perepichka, M. Bendikov, J. Am. Chem. Soc., 125

(2003) 15151-15162.

[6] V. G. Bairi, B. A. Warford, S. E. Bourdo, J. Appl. Poly. Sci., 124

(2012) 3320-3324.

[7] A. Acharya, R. Mishra, G. S. Roy, Arm. J. Phy., 3 (2010) 195-202.

[8] N. G. Deshpande, Y. G. Gudage, R. Sharma, Sensors Actuators B,

138 (2009) 76-84

[9] X. Zhang, Q. He, H. Gu, J. Mater. Chem. C, 1 (2013) 2886.

[10] J. Zhu, S. Wei, L. Zhang, J. Mater. Chem., 21 (2011) 3952-3959.

[11] D. Kelkar and A. Chourasia, Chem. Chem. Tech., 5 (2011) 309-315.

[12] B. Manjunath, A. Venkataraman, T. Stephen: J. Appl. Polym. Sci.,

17 (1973) 1091.

[13] D. Kelkar and A. Chourasia, Chemistry and chemical technology, 5

(2011) 310-315.

[14] X. Zhang, J. Zhang, Z. Liu, et al. Chem. Comm., 16 (2004) 1852-

1853.

136

[15] J. Huang, R. B. Kaner, Angew Chem Int Ed, 43 (2004) 5817-5821.

[16] X. Zhang, S. Wei, N. Haldolaarachchige, J. Phys. Chem. C, 116

(2012) 15731-15740.

[17] G. X. Zhi, K. Y. Fei, Y. T. li, Nonferrous Met. Soc.China, 22 (2012)

380−385.

[18] B. D. Boer, P. F. V. Hutten, L. Ouali, Macromolecules., 35 (2002)

6883-6892.

[19] H. T. Santoso, V. Singh, K. Kalaitzidou, Acs Appl. Mater.

Interfaces, 4 (2012) 1697−1703.

[20] S. Koul, R. Chandra, S. K. Dhawan, Sensors Actuators B, 75 (2001)

151-159.

[21] H. S. Moon, and J. K. Park, Macromolecules, 31 (1998) 6461-6468.

[22] G. A. Rimbu, I Stamatin,. C. L. Jackson, Scott, J. Optoelec. Adv.

Mate., 8 (2006) 670-674.

[23] J. U. Lee, J. W. Jung, T. Emrick, Nanotechnology, 21 (2010) 1-9.

[24] H. Kobe, K. Ohnaka, H. Kato, Vac. Sci. Technol. A, 31 (2013)

011504.

[25] M. He, J. Ge, M. Fang, F. Qiu, Y. Yang, Polymer, 51 (2010) 2236-

2243.

[26] B. D. Boer, P. F. V. Hutten, L. Ouali, 35 (2002) 6883-6892.

[27] H. T. Santoso, V. Singh, K. Kalaitzidou, Acs. Appl. Mater

Interfaces, 4 (2012) 1697−1703.

[28] S. Koul, R. Chandra, S. K. Dhawan, Sensors Actuators B, 75 (2001)

151-159.

137

[29] H. S. Moon, and J. K. Park, Macromolecules, 31 (1998) 6461-6468.

[30] G. A. Rimbu, I. Stamatin, C. L. Jackson, Scott J. Optoelec.

Advanced Materials, 8 (2006) 670-674.

[31] J. U. Lee, J. W. Jung, T. Emrick, Nanotechnology, 21 (2010) 1-9.

[32] H. Kobe, K. Ohnaka, H. Kato, Vac. Sci. Technol. A, 31 (2013)

011504.

[33] M. He, J. Ge, M. Fang, F. Qiu, Y. Yang, , Polymer, 51 (2010) 2236-

2243.

[34] J. H. Lim, N. Phibolsirichit, S. Mubeen, Nanotechnology, 21 (2010)

075502.

[35] J. B. M. Krishna, A. Saha, G. S. Okram, J. Phys. D: Appl. Phys., 42

(2009) 095404.

138

Chapter 3

[1] P. C. Rodrigues, M. P. Cantao, Eur. Poly. Journal, 38 (2002) 2213-

2217.

[2] V. G. Bairi, B. A. Warford et. al 35 (2011) 242.

[3] J. Zhu, S. Wei, L. Zhang, J. Mater. Chem., 21 (2011) 3952

[4] Y. F. Lim, J. J. Choi, T. Hanrath, J. Nanomater, 6 (2012) 2118-2127.

[5] B. Balamurugan, B. R. Mehta, Thin Solid Films, 396 (2001) 90–96.

[6] J. Ghijsen, L. H. Tjeng, J.V. Elp, Phys Rev B, 38 (1998) 11322.

[7] A. Cruccolini, R. Narducci, Sensors Actuat. B: Chem., 98 (2004)

227–232.

[8] V. R. Katti, A. K. Debnath, Sens. Actuat. B: Chem., 96 (2003) 245–

252.

[9] K. H. Muller, High-Tc Superconductors and Related Materials.

Dordrecht,The Netherlands: Kluwer, (2001).

[10] H. Fan, L. Yang, W. Hua, Nanotechnology, 15 (2004) 37–42.

[11] A. Santos, P. Yustos, Appl. Catal. B: Environ., 60 (2005) 323–333.

[12] A. A. Ponce, K. J. Klabunde, A: Chem., 225 (2005)1–6.

[13] C. T. Hsieh, J. M. Chen, H. H. Lin, Appl. Phys. Lett.,83 (2003)

3383.

[14] B. T. Raut, M. A. Chougule, R. C. Pawar, J. Mater Sci Mater

Electron, 23 (2012) 2104–2109.

[15] L. Zhang, W. Lu, Y. Feng, Acta. Phys. Chim. Sin., 24 (2008) 2257–

2262.

139

[16] J. Huang, R. B. Kaner, J. Am. Chem. Soc, 126 (2004) 851.

[17] X. Zhang,W. J. Goux, S. K. Manohar, J. Am. Chem. Soc.,126 (2004)

4502.

[18] M. Matsuguchi, J. Io, G. Sugiyama, Y. Sakai, Synth Met, 15 (2002)

128.

[19] A. RiulJr, A. M. Gallardo Soto, L. H. C. Mattoso, Synth. Met., 132

(2003) 109.

[20] J. Morales, L. Sanchez, F. Martin, Electrochimica ACTA, 49 (2004)

4589-4597.

[21] A. Debart, L. Dupont, Poizot, J. Electro. Society, 148 (2001)1266-

1274.

[22] J. Zhou, L. Ma, H. Song, Chem. Comm., 13 (2011) 1357-1360.

[23] H. Zengin, Kalayc, G. Mater. Chem. Phys., 120 (2010) 46.

[24] S. Sinha, S. Bhadra, D. Khastgir, J. Appl. Polym. Sci., 112 (2009)

3135.

[25] W. Shen, M. Shi, M. Wang, H. Chen, Mater. Chem .Phys.122 (2010)

588.

[26] S. Kazim, Ali, V. Zulfequar, M. Curr. Appl. Phys. 7 (2007) 68.

[27] A. Tripathi, K. P. Misra, R. K. Shukla, J. Appl. Poly. Sci., accepted 7

April 2013; Published online 00 Month 2013

[28] D. K. Bandgar, G. D. Khuspe, R. C. Pawar, Appl. Nanosci., 4 (2014)

27-36.

[29] S. Deivanayaki, V. Ponnuswamy, Polymer, 49 (2012)10182-1018.

140

[30] K. H. Lee, H. Y. Kim, Y. M. La, Polym. Phys, 40 (2002) 2259–

2268.

[31] Y. G. Han, T. Kusunose, T. Sekino, Synth. Met, 159 (2009) 123–

131.

[32] R. M. Silverstein, F. X. Webster, John Wiley & Sons Inc., New

York, (1998)

[33] G. D. Khuspe, S. T. Navale, M. A. Chougule, Ele. Mater Lett, 178

(2013) 1-9.

[34] S. Ivanov, P. Mokreva, V. Tsakova, Thin Solid Films, 441 (2003)

44–49.

[35] D. M. Jundale, P. B. Joshi, J. Mat. Sci Mat. Electron., 23 (2012)

1492–1499.

[36] P. Mitra, J. Phys. Sci., 14 (2010) 235–240.

[37] S. K. Singh, A. K.Verma, R. K. Shukla, IJMITE, 2 ( 2014) 85-92.

[38] S. M. Hassan, A. G Baker, Int. J. Basic App. Sc. 01 (2012) 352-362.

[39] S. Ameen, V. Ali, M. Zulfequar, J.of App. Poly. Sc.,112 (2009)

2315–2319.

[40] Y. Haba, E. Segal, M. Narkis, A.. Synth Met, 106 (1999) 59–66.

[41] D. Jundale, S. Pawar, M. Chougule, J Sens Technol, 1 (2011) 36–46.

141

Chapter 4

[1] M. Matsuguchi, J. Io, G. Sugiyama, Y. Sakai, Synth. Metals, 128

(2002) 15–19.

[2] R. Rella, P. Siciliano, F. Quaranta, Sens. Act. B, 68 (2000) 203–209.

[3] M. K. Ram, O. Yavuz, M. Aldissi, Synthetic Metals, 151 (2005) 77–

84.

[4] S. Richard, P. Gnanakan, M. Rajasekhar, Int. J. Elect.Sci., 4 (2009)

1289–1301.

[5] H. Meng, D. F. Perepichka, M. Bendikov, J. Am. Chem. Soc., 125

(2003) 15151-15162.

[6] R. Ansari,. 3 (2006) 186-201.

[7] J. Mattan, A. Uusimaki, H. Torvela, Chem. Macr. Symp., 22 (1988)

161-190.

[8] A. J. Y. Talaie Lee, et. al. ThinSolid Films, 363 (2000) 163-166.

[9] M. Natalie, R. R. J. Mortimer, Sc. progress, 85 (2002) 243-262.

[10] L. H. M. Krings, E. E. Havinga, J. J. M. Donkers, Synth. Metals, 54

(1993) 453-459.

[11] S. B. Adeloju, S. J. Show, Anal. Chi. Acta, 281 (1993) 611-627.

[12] J. M. Slater, E. J. Watt, Analytical proceeding, 26 (1989) 397-399.

[13] S. Sukeerthi, et. al, Ind. J. Chem, 33 (1994) 565-571.

[14] H. Ge, P. R. Teasdale, G. G. Wallace, J. Chromat., 544 (1991)305-

316.

142

[15] N. Mermilliod, J. Tanguy, J. Electrochem. Soc., 133 (1986) 1073-

1079.

[16] A. Mirmohseni,W. E Price, H. Zhao, J. Iint. Syst. Struct., 4 (1993)

43-49.

[17] R. Ansari, E. J. Chem., 3 (13) (2006) 186-201.

[18] J. Zhu, S. Wei, L.Zhang, Z. Guo, J. Mater. Chem., 21 (2011) 3952.

[19] P. C. Rodrigues, M. P. Cantao, P. Janissek, Eur. Poly. J., 38 (2002)

2213-2217.

[20] G. A. Rimbu, I. Stamatin, C. L. Jackson, J. Opto. Adv. Mat. 8 (2006)

670-674.

[21] J. H. Lim, N. Phibolsirichit, S. Mubeen, Nanotech., 21 (2010)

075502.

[22] M. C. Arenas, G. Sancez, M. E. Nicho, Appl. Phy. A, 106 (2012)

901-908.

[23] A. G. MacDiarmid, A. J Epstein. Synth. Met., 68 (1994) 65103.

[24] G. P. Gardini, Adv Hetrocycl. Chem., 15 (1973) 67.

[25] J. Harreld, H. P. Wong, B. C. Dave, Crystalline Solids, 225 (1998)

319-324.

[26] M. Taunk, A. Kapil, S. Chand, The Open Macro. Journal, 2 (2008)

74-79

[27] J. C. Vidal, E. Garcia, J. R. Castillo, Anal. Chim. Acta, 385 (1999)

213-222.

143

[28] T. E. Campbell, A. J. Hodgson, G. G.Wallace, Electro., 11 (1999)

215-222.

[29] E. Smela, J. Micro. Micro., 9 (1999) 1-18.

[30] T. A. Skotheim, R. Elsenbaumer, Hand-Book Conducting Polymers,

Marcel Dekker, New York, (1998).

[31] G. G. Wallace, G. Spinks and P. R. Teasdale, Conductive

Electroactive Polymers, Technomic, New York, (1997).

[32] J. O. Iroh, C. Williams, Synthetic Metals, 99 (1999) 1-8.

[33] W. K. Jang, J. Yun, H. Kim, Carbon Letters, 13 (2012) 88-93.

[34] L. Jiang, H. K. Jun, Y. S. Hoh, Sen. and Act. B, 105 (2005) 132–

137.

[35] H. K. Jun, Y. Hoh, B. Lee, Sensors and Actuators B, 96 (2003) 576–

581.

[36] J. Zhu, S. Wei, L. Zhang, J. Mater. Chem., 21 (2011) 3952-3959.

[37] A. Diaz, J. Bargon, H. Cond. Poly., 1 (1986) 82-100.

[38] B. K. Moss, R. P. Burford, Material Forum, 13 (1993) 35-42.

[39] T. H. Chao, J March, J. Polymer Science, 26 (1988) 743-753.

[40] A. Mohhammadi, I. L. Salaneck , Synthetic Metals, 21 (1987) 169-

173.

[41] L. F. Warren, D. P. Anderson, Ele. Society, 134 (1987) 101-105.

[42] S. P. Armes, B. Vincent, J. Chem. Soc., 134 (1987) 287-294.

[43] H. Eisazadeh, G. Spinks, G. G. Wallace, Material Forum, 16 (1992)

341-344.

144

[44] V. Bocchi, G P Gardini, J. Mat. Science Letters, 6 (1987) 1283-

1284.

[45] J. Zhu, S. Wei. L. Zhang J. Mater. Chem., 21 (2011) 3952.

[46] J. B. M Krishna, A. Saha, G. SOkram, Phys. D: Appl. Phys., 42

(2009) 095404.

[47] K. P Misra, R. K Shukla, Appl. Phys. Lett., 95 (2009) 031901.

[48] N. V. Hieu, N. Q. Dung, Sens. Actu. B, 140 (2009) 500.

[49] E. A. Bazzaoui, S. Aeiyach and P. C. Lacaze, J. Electroanal. Chem.,

364 (1994) 63–69.

[50] A. Faulques, W. Wallnoefer and H. Kuzmany, J. Chem. Phys. 90

(1989) 7585–7595.

[51] S. Koul, R Chandra Dhawan, S. K.Sens. Actuators B, 75 (2001)

151.

[52] V.G.Bairi,B.AWarford,S.E.Bourdo.J. Appl. Polym.Sci.,124 (2012)

3320.

[53] H. S Moon and J. K Park,.Macromolecules, 31 (1998) 6461.

[54] S.Ameen,G.B.Lakshmi,M.Husain,.J.Phys.D:Appl.Phys. 42 (2009)

105104.

[55] N. Mukherjee, B. Show, S.K. Maji, Mater.Lett.,65 (2011) 3248-

3250.

[56] S. Ameen, V. Ali, M. Zulfequar J. Polym. Sci.,106 (2007) 21265.

[57] S.Ameen, V. Ali, M. Zulfequar,J.App. Polym.Sci., 112 (2009)

2315–2319

145

Chapter 5

[1] T Skothemin and R Elsenbaumer 1998 Handbook of Conducting

Polymers.

[2] Z.Hua ,J. Shi, L .Zhang, M Ruan , Adv. Mater.,106 (2002) 14830

[3] A Rothschold and Y Komem Appl. Phys. Lett, 82 (2003) 574.

[4] C. Paula. Rodrigues,MauricioP.Cantao…European polymer journal,

38 (2002) 2213-2217

[5] J. C. Vidal, E. Garcia and J. R. Castillo,AnalyticaChimicaActa, 385

(1999) 213-222.

[6] T. E. Campbell, A. J. Hodgson and G. G. Wallace,Electroanalysis, 11

(1999) 215-222.

[7] E. Smela,J.l of Micr. and Micro., 9 (1999) 1-18.

[8] T. A. Skotheim, R. Elsenbaumer, Marcel Dekker, New York, 1998.

[9] G. G. Wallace, G. Spinks and P. R. Teasdale,Technomic, New York,

1997.

[10] J. O. Iroh and C. Williams,Synthetic Metals, 99 (1999) 1-8.

[11] W. K. Jang, J. Yun, H. Kim,, Carbon Letters,13 (2012) 88-93.

[12] L. Jiang, H. K. Jun, Y. S. Hoh, Sen. and Actu. B, 105 (2005) 132–

137.

[13] H. K. Jun, Y. Hoh, B. Lee, Sensors and Actuators B, 96 (2003) 576–

581.

[14] V.Gopal Bairi, A. Brock warford, j. App. Poly. Sc.,124 (2011)

35242.

146

[15] Li Li, Zifeng Yan…Journal of Natural Gas Chemistry, 14 (2005)

35-39.

[16] G A. Rimbu ,I Stamatin, J.of optoele. Adv. Mat.,8 (2006) 670-674.

[17] J. Zhu, S. Wei, L Zhang, , J. Mater. Chem., 21 (2011) 3952.

[18] J Zhu, S Wei. L Zhang.Y Mao, Ryu J. Mater. Chem., 21 (2011)

3940.

[19] P.C.Rodrigues, M.P.Cantao, Janissek, Eur. Polym. J., 38 (2002)

2213.

[20] G. A Rimbu, I.Stamatin, J Optoelectron. Adv. Mater., 8 (2006) 670.

[21] J. H Lim,N Phibolsirichit, S Mubeen; Nanotechnology,21 (2010)

075502.

[22] M.C Arenas,G. Sancez,M.E. Nicho, Appl. Phy.A,106 (2012) 901-

908.

[23] G. K Prasad, T. P Radhakrishnan,Kumar, Sens. Act. B, 106 (2005)

626.

[24] M Matsuguchi ; Asahi, T.Sens. Actuators B, 160 (2011) 999.

[25] S Koul, R Chandra, S Dhawan,K.Sens. Actuators B, 75 (2001) 151.

[26] K. R.J. NemadeSens. Transducers , 135 (2011) 110.

[27] S Ameen,V Ali, M Zulfequar,J. Appl. Polym. Sci., 112 (2009) 2315.

[28] M Matsuguchi,J Io,G Sugiyama, Y Sakai,.Synth. Met., 128 (2002)

15.

[29] P. Saini, V. Choudhary, B. P. Singh, Mater Chem Phys,113 (2009)

919-926.

147

[30] M. I. Khan, A. U. Chaudhary, S. Hashim, Chem. Eng. Res. Bull., 14

(2010) 73-86.

[31] I. D. Sharma,V. K. Sharma, S. K. Dhawan, Ind. J. P. Appl Phys,50

(2012) 184-187.

[32] S. Sukeerthi, and A. Q. Contractor, Indian J. Chem, 33 (1994) 565-

571.

[33] H. Ge, P. R. Teasdale and G. G. Wallace, J. Chrom., 544 (1991) 305-

316.

[34] N. Mermilliod and J. Tanguy, J. Electrochem. Soc., 133 (1986)

1073-1079.

[35] A. Mirmohseni, W. E. Price, G. G. Wallace, Intelligent Material

Systems and Structures, 4 (1993) 43-49.

[36] A. Diaz and J. Bargon "Handbook of Cond. Polymers", 1 (1986) 82-

100.

[37] B. K. Moss, R. P. Burford, Material Forum, 13 (1993) 35-42.

[38] T. H. Chao and J. March, J. Polymer Science:, 26 (1988) 743-753.

[39] A. Mohhammadi, I. Lundstrom, Synthetic Metals, 21 (1987) 169-

173.

[40] J. Zhu, S. Wei, L. Zhang, J. Mater. Chem., 21 (2011) 3952-3959.

[41] J. Zhu, S. Wei, X. Chen, A. B. Karki, D. Rutman, D. P. Young and

Z. Guo, J. Phys. Chem. C, 114 (2010) 8844–8850.

[42] J. B. M. Krishna, A. Saha, G. S. Okram, J. Phys. D: Appl. Phys., 42

(2009) 095404.

148

[43] A. Tripathi, K. P. Misra, R. K. Shukla, J. App. Poly. Sci, 130 (2013)

1941-48.

[44] K. R. Nemade, Sensors & Transducers Journal, 135 (2011) 110-117.

[45] S. Ameen, V. Ali, M. Zulfequar, J. App. Poly. Sci, 112 (2009)

2315-2319.

[46] J. Vivekanandan, V. Ponnusamy, Arch. App. Sci. Res., 3 (2011)

147-153.

[47] J. Zhu, Suying Wei, Lei Zhang,Yuanbing Mao, J.Mater.Chem., 21

(2011) 3952

[48] M. RE Inoue Navarro, M.B. Inoue, Synth. Met, 30 (1989) 199.

[49] P. Srinivasan, J. Amalraj, A. Nath, J. Mol. Cat. A: Chem., 218

(2004) 47.

[50] X.-R. Zeng and T.-M. Ko, J. Polym. Sci., Part B: Polym. Phys., 35

(1997) 1993–2001.

[51] S. Quillard, G. Louam, J. P. Buisson, Synth. Met., 84 (1997) 805–

806.

[52] M. Arora, S. K. Gupta, AIP Conf Proc, 1075 (2008) 118.

[53] S. Koul, R. Chandra, S. Dhawan, Sens. Actuators B, 75 (2001) 151.

[54] J. Zhu, S. Wei, L. Zhang, J. Mater. Chem., 21 (2011) 3952.

[55] H. S. Moon and J. K. Park, Macromolecules, 31 (1998) 6461.

[56] S. Ameen, G. B. V. S Lakshmi, M. Husain, Appl. Phys., 42 (2009)

105104.

149

[57] A. Srivastava, R. K. Shukla and K. P. Misra, Cryst. Res. Technol.,

46 (2011) 893-898.

[58] K. P. Misra, R. K. Shukla, A. Srivastava, Appl. Phys. Lett., 95

(2009) 031901.

[59] Z. R. Khan, M. S. Khan, M. Zulfequar, Mat. Sci. Appl., 2 (2011)

340.

[60] S. Singh, G. M. Singh, P. C. Pandey, R. Prakash, Sens. Actu. B, 132

(2008) 99-106.

150

Chapter 6

[1] A. G. MacDiarmid, A. J. Epstein. Synth. Met., 65 (1994) 103.

[2] B. H. Kim, D.H. Park, J. Joo, Synth. Met., 150 (2005) 279–284.

[3] M. R. Mahmoudian, Y. Alias, W.J. Basirun, Mate. Chem and Phy.,

124 (2010) 1022–1028.

[4] A. Asan, M. Kabasakaloglu, M. L. Aksu, Rus. J. Electro., 41 (2005)

175–180.

[5] M. K. Ram, M. Adami, P. Faraci, Nicolini, C. Poly., 41 (2000) 7499.

[6] E. J. Oh, K. S. Jang, Synth. Met., 119 (2001) 109.

[7] R. Ansari, E. J. of Chem., 3 (2006) 186-201.

[8] J.Harreld, H.P.Wong, B.C.Dave, J. Non. cryst.sol., 225 (1998) 319-

324.

[9] P. Xu, X. Han, C. Wang, J. of Phy. Chemistry B, 112 (2008) 10443–

10448.

[10] M.R. Mahmoudian, W.J. Basirun, Y. Alias, Progress in Organic

Coatings, 71 (2011) 56–64.

[11] S. Sathiyanarayanan, S. Syed Azim, G. Venkatachari, Elect.Acta, 52

(2007) 2068–2074.

[12] O. Zubillaga, F.J. Cano, I. Azkarate, Surface and Coatings

Technology, 202 (2008) 5936–5942.

[13] J. Mattan, A. Uusimaki, H. Torvela Chem., Macr. Symp., 22 (1988)

161-190.

[14] A. J. Y. Talaie, Y. K Lee, J. Lee Jang, Thin Solid Films, 363 (2000)

163-166.

[15] Phillips, G. Lance, and Barbano, J. Dairy Sci., 80 (1997) 2726.

[16] S. Sukeerthi and A. Q. Contractor, In. J. Chem, 33 (1994) 565-571.

151

[17] H. Ge, P. R.Teasdale and G. G. J. Chromatography, 544 (1991) 305-

316.

[18] N. Mermilliod and J. Tanguy, J. Electrochem. Soc.,133 (1986) 1073-

1079.

[19] A. Mirmohseni, W. E. Price, J. int. Mat. Syst. Struct., 4 (1993) 43-

49.

[20] A. Diaz and J. Bargon, Handbook of Conducting Polymers, 1(1986)

82-100.

[21] B. K. Moss, R. P. Burford, Material Forum, 13 (1993), 35-42.

[22] T. H. Chao, J. March, J. Poly. Sci., 26 (1988) 743-753.

[23] A. Mohhammadi, I. Lundstrom, Synthetic Metals, 21(1987)169-173.

[24] L. F. Warren, D. P. Anderson, Electrochem. Soci., 134 (1987) 101-

105.

[25] S. P. Armes, B. Vincent, J. Chem. Soc., Chem. Commun., (1987)

287-294.

[26] H. Eisazadeh, G. Spinks, Material Forum, 16 (1992) 341-344.

[27] V. Bocchi, G. P. Gardini, S. Rapi, J. Mat. Sc. Lett., 6 (1987)1283-

1284.

[28] S. Deivanayaki, V. Ponnuswamy, Elixir Polymer, 49 (2012)10182-

10185.

[29] Y. J. Kwon, K. H. Kima, C. S. Limb, J. Ceram. Process. Res. 3

(2002)146-149.

152

[30] A. Tripathi, K. P. Misra, R. K. Shukla, J. App. Poly. Sci, 130

(2013)1941-48.

[31] H. Ali. Gemeay, A. Ikhlas Mansour, Europen Polymer Journal,

41(2005) 2575-2583.

[32] J. Vivekanandan, V. Ponnusamy, Arch. Appl. Sci. Res., 3 (2011)

147-153.

[33] K. R. Nemade, Sensors & Trans. J., 135 (2011) 110-117.

[34] S. Ameen, V. Ali, M. Zulfequar, J. App. Poly. Sci., 112 (2009)

2315-2319.

[35] X. Lu, D. Zhao, C. Wang, Rapid Comm., 27 (2006) 76.

[36] Lu Xiaofeng, Zhao Qidong, Liu Xincai, Macromol. Rapid

Commun., 27 (2006) 430–434.

[37]M. R. Mahmoudian, W. J. Basirun, Appl. Surf. Sci., 257 (2011)

8317– 8325.

[38] R. N. Mohammad, Ali Akbar Entezami, J. Appl. Poly. Sci., 94

(2004) 254–258.

[39] S. K. Singh, A. K. Verma, R. Lakhan, R. K. Shukla, Inter. J.

Manag., Info. Tech. Eng., 2 (2014) 85-92.

[40] S. Deivanayaki, V. Ponnuswamy, P. Jayamurugan, S. Ashokan,

Elixir Polymer, 49 (2012) 10182-10185.

[41] A. A. Entezami, M. Reza Nabid, J. App. Poly. Sci., 94 (2004) 254–

258.

[42] D. Y. Godovsky, A. E. Varfolomeev, D. F. Zaretsky, J. Mater.

Chem., 11 (2001) 2465–2469.

153

Fig. (a): Spin coating Unit

154

Fig. (b): Magnetic Stirrer with Hot Plate

155

Fig. (c): Weighing Unit

156

Fig. (d): Motorized Furnace Unit

157

Fig. (e): Hot Air Oven Unit

158

Fig. (f): Photoluminescence Unit

159

Fig. (g): UV-visible absorption Unit

160

Fig. (h): FTIR Spectroscopy Unit

161

Fig. (i): Hydraulic Press Machine Unit