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SYNTHESIS AND CHARACTERIZATION OF
POLYANILINE CO-DOPED WITH POLYVINYL
ALCOHOL AND TRANSITION METALS
Ph.D Thesis
By
RIZWAN ULLAH
INSTITUTE OF CHEMICAL SCIENCES
UNIVERSITY OF PESHAWAR PAKISTAN
(OCTOBER, 2014)
SYNTHESIS AND CHARACTERIZATION OFPOLYANILINE CO-DOPED WITH POLYVINYL
ALCOHOL AND TRANSITION METALS
BY
RIZWAN ULLAH
DISSERTATION
SUBMITTED TO THE UNIVERSITY OF PESHAWAR IN THE PARTIALFULFILLMENT OF THE REQUIREMENTS OF THE DEGREE OF
DOCTOR OF PHILOSPHY IN CHEMISTRY
INSTITUTE OF CHEMICAL SCIENCES
UNIVERSITY OF PESHAWAR PAKISTAN
(OCTOBER, 2014)
INSTITUTE OF CHEMICAL SCIENCES
UNIVERSITY OF PESHAWAR, PAKISTAN
APPROVAL SHEET
Certified that Mr. Rizwan Ullah S/O Shakir Ullah has carried out his research and experimental
work on the topic entitled as “Synthesis and Characterization of Polyaniline Co-Doped with
Polyvinylalcohol and Transition Metals” under our guidance and supervision. His research
work is original and his dissertation is worthy of presentation to the University of Peshawar for
the award of degree of Doctor of Philosophy in Chemistry.
______________________ _______________________
SUPERVISOR CO-SUPERVISOR
Prof. Dr. Khurshid Ali Dr. Anwar-Ul-Haq Ali Shah
Institute of Chemical Sciences, Institute of Chemical Sciences,
University of Peshawar, Pakistan University of Peshawar, Pakistan
_________________________ _______________________
Dr. YOUSAF IQBAL EXTERNAL EXAMINAR
Professor & Director
Institute of Chemical Sciences,
University of Peshawar Pakistan
i
Dedication
To my teachers & my mentors
Prof. Dr. Khurshid Ali and Dr. Anwar-Ul-Haq Ali Shah
Without whom this work would never have come into being.
To those flanking to me
My Parents, My Brothers, My Sisters & My Wife
Whose love, patience, support and encouragement stay with
me throughout my life.
To my Lovely Daughter
Fatima Aiman
Whose love is priceless to me and will always endure me.
ii
Acknowledgements
All praise to Allah the Omniscient, who thought man what, he not knew, who equipped
his humble creature with mental facility, which enabled and encouraged me to complete
this work. Peace and blessing be upon Prophet Muhammad Salallaho Alaihy Wasallam,
his families, his relatives and all his followers.
A single flower cannot make a garden or a single star cannot make the beautiful shiny
sky. The same way a research work can never be the outcome of a single individual‘s
talent or effort. During my trip from objective to goal, I have experienced shower of
blessings, guidance and inspiration from my teacher’s parents and all my well-wishers.
Though it is not possible for me to name and thanks them all individually, but it is great
pleasure for me to pen down some of the distinct personalities who have made it
possible for me to put this research work in present form.
First and foremost, I take this opportunity to express my profound sense of gratefulness
to my venerated guide, mentor and my research supervisor, Prof. Dr. Khurshid Ali
whose flawless guidance, boundless enthusiasm, persevering nature, enlightening
discussion and valuable suggestion have enabled me to complete this work. Only
because of his support and inspiration I could confidently embark upon a research work
of such magnitude. I consider myself fortunate to have had the opportunity to work
under his guidance.
iii
I would like to express my deep sense of gratitude to Dr. Anwar –Ul-Haq Ali Shah
(Associate Professor); my research co-supervisor who encouraged me and who has
shown keen interest in my assignment and has inspired me and render self less support
throughout this investigation. I appreciate all his contributions of time and ideas to make
my Ph.D. experience productive and inspiring. The joy and enthusiasm he has for
research work was contagious and motivational for me.
I am truly grateful to both of them. I can’t thank them enough, but I pray Allah, to bless
them for their exertions and reward them according to His generosity.
I would also like to acknowledge the contributions, advice and suggestions of my foreign
supervisors Dr. Jadranka Travas Sejdic and Prof. Dr. Graham A. Bowmaker who
supported me during the six month research at the Polymer Electronic Research Centre
(PERC) University of Auckland, New Zealand.
I gratefully acknowledge the Higher Education Commission of Pakistan for financial
support and providing me a tremendous opportunity to complete my research work at
the Institute of Chemical Sciences, University of Peshawar through Indigenous Ph.D
Fellowship Program and at the Polymer Electronic Research Centre (PERC) University
of Auckland, New Zealand, through International Research Support Initiative Program.
Mention must be made of my worthy professors and teachers at the Institute of
Chemical Sciences who have helped me in various ways. For this, I am truly blessed.
iv
I would like to express my sincere thanks to Dr. Yousaf Iqbal., Professor and Director
Institute of Chemical Sciences University of Peshawar, for the support he gave me
along the way.
Very special thanks and my deep gratitude go to Dr. Sher Khan, Moeen Ul Amin,
Ahmad Bilal, Umar Javed, Waseem Ahmad, Azan Meer, and Mohy Uddin Khan Khattak
for their support during my stay at Newzealand.
I would like to thank Dr. Habib-Ur-Rehman, Dr. Fazlullah Khan Banghash and Dr. Atta-
Ur-Rehman teaching faculty member of physical section, for their support during my
work. I want to extend my special thanks to Dr. Salma Bilal for providing me help and
support in my work.
I am grateful to my senior scholar colleagues for providing a stimulating and decent
environment to learn and grow. Many thanks to Dr. Inayatullah, Dr. Nasir Ullah, Dr.
Hamid Hussain, Dr. Abdul Hameed, Dr. Andaleeb Azam and Dr. Behisht Ara.
My time at the institute was made enjoyable in large part due to my colleagues and
friends. I am grateful to Mr. Muhammad waqas, Mr. Imran Ullah, Ms. Shanaz Pir
Muhammad, Ms. Aliya, Ms. Robila Nawaz, and Ms. Saima Shaheen. I cannot forget
Habib Ullah and Amir Muhammad who were always around me in my hard times.
I take this opportunity to acknowledge with thanks the help and support that I have
received from Mr. Ashfaq (Librarian ICS), Mr. Zaheer ud Din (store supervisor), Mr.
v
Muhammad Ali, Mr. Arif Ismail, Mr. Jangir Khan, Mr. Ilyas Khan, Mr. Sajid Khan and all
the clerical and para teaching staff of Institute of Chemical Sciences.
I want to express my sincere gratitude to my great father and mother who suffered a lot
to keep me free from domestic responsibilities and their prayers, guidance, and sound
advice have inspired and sustained me throughout my academic and personal life. I pay
a profound appreciation to my brothers; Zakir Hussain and Muhammad Fawad, to my
humble and simple sisters, to my uncle, Gulzar Ahmad, and of course my sweet and
lovely daughter Fatima Aiman whose love is invaluable to me and will always sustain
me. I love you all!
Words fail to express the endurance with which my loving wife bore my absence. She
offered determined patience, love, support and confidence in me, for which there is no
adequate way to express my appreciation.
Last but not least, I owe gratitude and thankfulness to all who were involved directly or
indirectly, knowingly or unknowingly to reach in the venture of mine.
Rizwan Ullah
University of Peshawar
October 2014
vi
Table of Contents
S.No Title P. No.
Dedication i
Acknowledgment ii
Table of content vi
List of tables xi
List of figures xii
List of abbreviations xv
List of publications xviii
Abstract xix
1 CHAPTER 1. INTRODUCTION 1
1.1 Literature review 2
1.2 Polyaniline 11
1.2.1 Structure of Polyaniline 11
1.2.2 Conductivity of polyaniline (PANI) 12
1.2.3 Mechanism of Conductivity 13
1.2..4 Synthesis of Polyaniline (PANI) 15
1.2.5 Mechanisms of polymerization 16
1.2.6 Doping of PANI 18
1.3 Characterization of PANI 19
1.3.1 UV/Visible spectroscopy 19
1.3.2 FTIR spectroscopy 20
1.3.3 X-ray diffraction (XRD) 20
1.3.4 Cyclic voltammetry 21
1.3.5 Scanning electron microscopy (SEM) 22
1.3.6 Elemental analysis 22
1.4 Solubility of PANI 23
1.5 Polymerization of substituted aniline 24
1.5.1 Copolymerization of aniline 24
vii
1.5.2 PANI blends 25
1.5.3 PANI doped with surfactants 25
1.5.4 Composites of PANI 26
1.6 Aims and objectives of the work 26
2 CHAPTER 2. EXPERIMENTAL 28
2.0 Experimental (Part I) Synthesis and Characterization of Polyanilineby using CuCl2 as Oxidizing agent
28
2.1 Materials 28
2.2 Procedure 28
2.3 Dedoping of B-PANI and H-PANI 29
2.4 Reduction of PANI, DB-PANI and DH-PANI 29
2.5 Characterization 29
2.5.1 FTIR Spectroscopy 29
2.5.2 UV/Vis Spectroscopy 30
2.5.3 Elemental Analysis 30
2.5.4 X-ray Photoelectron Spectroscopy (XPS) 30
2.5.5 Near Edge X-ray Absorption Fine Structure (NEXAFS)
Spectroscopy
30
2.5.6 Solid-state NMR 31
2.5.7 SEM analysis 31
2.6 Experimental (Part II) Synthesis and characterization of
leucoemeraldine
31
2.6.1 Materials 31
2.6.2 Procedure 31
2.6.3 Characterization 32
2.6.3.1 FTIR Spectroscopy 32
2.6.3.2 UV/Vis Spectroscopy 32
2.6.3.3 Elemental Analysis 32
2.7 Experimental (Part III) Synthesis and characterization of polyanilinedoped with Cu II chloride by inverse emulsion polymerization
33
viii
2.7.1 Materials 33
2.7.2 Procedure 33
2.7.3 Characterization 33
2.7.3.1 Conductivity measurements 33
2.7.3.2 UV/Vis spectroscopy 34
2.7.3.3 FTIR spectroscopy 34
2.7.3.4 Thermo gravimetric analysis (TGA) 34
2.7.3.5 X-ray diffraction (XRD) 34
2.7.3.6 Scanning electron microscopy 34
2.7.3.7 Cyclic voltammetry 34
2.8 Experimental (Part IV) Synthesis and Characterization of
Polyaniline Doped with Polyvinylalcohol by Inverse Emulsion
Polymerization
35
2.8.1 Materials 35
2.8.2 Procedure 35
2.8.3 Characterization 35
2.8.3.1 Conductivity measurements 36
2.8.3.2 UV/Vis spectroscopy 36
2.8.3.3 FTIR spectroscopy 36
2.8.3.4 Thermo gravimetric analysis 36
2.8.3.5 X-ray diffraction (XRD) measurements 36
2.8.3.6 Scanning electron microscopy (SEM) 36
2.8.3.7 Cyclic voltammetry 37
2.9 Synthesis and Characterization of Polyaniline Co-doped withPolyvinylalcohol and Cu by Inverse Emulsion Polymerization
37
2.9.1 Material 37
2.9.2 Procedure 37
ix
2.9.3 Characterization 38
2.9.3.1 Conductivity and mass measurement 38
2.9.3.2 UV/Vis spectroscopy 38
2.9.3.3 FTIR spectroscopy 38
2.9.3.4 Thermo gravimetric analysis 38
2.9.3.5 X-ray diffraction 38
2.9.3.6 Scanning electron microscopy 38
2.9.3.7 Cyclic Voltammetry 39
3 CHAPTER 3. RESULTS AND DISCUSSION 40
3.1 pH measurement and mass yield calculations 40
3.2 FTIR Spectroscopy 42
3.3 UV/Vis Spectroscopy 45
3.4 Elemental Analysis 47
3.5 X-Ray Photoelectron Spectroscopy 48
3.6 Soft X-ray Spectroscopy 53
3.7 Solid state NMR 54
3.8 SEM analysis 56
3.9 Mechanism of PANI fabrication 57
3.10 Results and discussion Part (II) 58
3.11 pH measurements and along with mass yield 58
3.12 FTIR Spectroscopy 58
3.13 UV/Vis Spectroscopy 59
3.14 Elemental Analysis 60
3.15 Results and discussion (Part III) 61
3.16 Mass yield and conductivity measurements 61
3.17 UV/Visible spectroscopy 61
3.18 FTIR spectroscopy 62
3.19 Thermogravimetric analysis (TGA) 63
3.20 X-ray diffraction (XRD) 64
x
3.21 Scanning electron microscopy (SEM) 65
3.22 Cyclic voltammetry (CV) 66
3.23 In situ UV/Vis spectroscopy 67
3.24 Results and discussion (Part IV) 71
3.25 Conductivity measurements and mass yield 71
3.26 UV/Visible spectroscopy 72
3.27 FTIR spectroscopy 72
3.28 Thermo gravimetric analysis (TGA) 73
3.29 X-ray diffraction (XRD) 74
3.30 Scanning electron microscopy (SEM) 75
3.31 Cyclic voltammetry (CV) 76
3.32 In situ UV/Visible Spectroscopy 77
3.33 Results and Discussion (Part V) 81
3.34 Conductivity Measurements and Mass Yield 81
3.35 UV/Visible Spectroscopy 82
3.36 FTIR Spectroscopy 82
3.37 Thermo gravimetric Analysis (TGA) 83
3.38 X-Ray Diffraction 84
3.39 SEM Analysis 86
4 CHAPTER 4. CONCLUSION 88
REFERENCES 91
xi
List of Tables
Table No. Table caption P. No.
1
Initial and Final Solution pH and Mass Yields for Reactionswith Various Oxidant to Monomer Ratios R
40
2
Weight (%) Loss of B-PANI after washing with HCl, NH4OHand N2H4 and corresponding Mass Yield of H-PANI, DB-PANIand PANIa 41
3
Compositions of DB-PANI and H-PANI for oxidant tomonomer ratio R = 15
48
4
Speciation of Nitrogen in PANI samples from N 1s PeakAnalysis
53
5
Peak assignment in the SSNMR of EB form of PANI
55
6
Oxidant to Monomer Ratio and Mass Yield along with initialand final pH
58
7
Elemental Analysis Results of L-PANI
60
8
Mass Yield and Conductivity of PANI and its Composites withCu
61
9
Mass Yield and Conductivity of PANI and its Composites withPVA
71
10
Mass Yield and Conductivity Measurements
81
xii
List of Figures
Fig. No. Figure caption P. No.
1Various redox states of PANI
12
2Interconversion of emeraldine base and emeraldine salt
13
3Radical cation formation and its resonance stabilization
16
4Conversion of radical cation to para-aminodiphenylamine
17
5Acid doping of PANI
18
6X-rays diffraction in a crystalline material
21
7FTIR spectrum of the initial product (R = 15) before washing
42
8
FTIR spectra of A(a) B-PANI, (b) H-PANI(c) PANI, B(a) DB-
PANI and (b) RB-PANI, C(a) PANI and (b) R-PANI, D(a) DH-
PANI and (b) RH-PANI.
43
9
UV/Vis spectra of A(a) B-PANI, (b) H-PANI, (c) PANI, B (a)DB-PANI (b) RB-PANI, C(a) PANI, (b) R-PANI, D(a) H-PANI,(b) DH-PANI and (c) RH-PANI
46
10Cu 2p XPS for (a) H-PANI, and (b) DB-PANI.
50
11N 1s XPS for (a) H-PANI, and (b) DB-PANI
52
12NEXAFS of (a) B-PANI (b) DB-PANI (c) RB-PANI
54
13
13C Solid State NMR spectra of DH-PANI55
14SEM analysis of (a) B-PANI, (b) H-PANI, and (c) DB-PANI
56
15Mechanism of PANI formation
57
16FTIR spectra of (a) pure EB (b) L-PANI
59
17UV/Vis spectra of (a) pure EB (b) L-PANI
60
18
UV/Vis spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4,(d) PANI-Cu 0.6 and (e) PANI-Cu 0.7
62
xiii
19
FTIR spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4,and (d) PANI-Cu 0.6.
63
20TGA analysis of (a) PANI (b) PANI-Cu
64
21XRD analysis of (a) PANI and (b) PANI-Cu
65
22SEM images of (a) PANI and (b) PANI-Cu
66
23CVS of (a) PANI and (b) PANI-Cu
67
24
UV-Vis spectra of (a) PANI and (b) PANI-Cu film, deposited onITO coated glass electrode, obtained at different electrodepotential values ranging from ESCE= 0.0 TO 0.8 V at an intervalof 0.1 V 68
25
(a) and (b) Absorbance vs. Potential at three selectedwavelengths, derived from the above displayed spectra in Fig. 24(a) and (b) 70
26UV/Vis spectra of (a) PANI and (b) PANI/PVA.
72
27FTIR spectra of (a) PANI and (b) PANI/PVA
73
28TGA curve of (a) PANI and (b) PANI/PVA
74
29XRD of (a) PANI and (b) PANI/PVA
75
30SEM images of (a) PANI and (b) PANI/PVA
76
31
CVs of (a) PANI and (b) PANI/PVA on gold foil electrode (vsSCE) in 0.5M H2SO4
77
32
UV/Vis spectra of (a) PANI and (b) PANI/PVA film, depositedon ITO coated glass electrode, obtained at different electrodepotential values ranging from ESCE= 0.0 TO 0.8 V at an intervalof 0.1 V 78
33
(a) and (b) Absorbance vs. Potential at three selectedwavelengths, derived from the above displayed spectra in Fig 32.(a) and (b). 80
34
UV/Vis spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and(d) PANI-Cu-PVA
82
35
FTIR spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA
83
36TGA analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA 84
xiv
37XRD analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA 85
38SEM images of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA 87
xv
LIST OF ABBREVIATIONS
% Percent
oC
cm-1
Degree celsius
Per centimeter
µm
γ
Micrometer
Gamma
µgL-1 Microgram per milliliter
APS Ammoniumpersulfate
AuNPs
β-NSA
BPO
CNT
Gold nanoparticles
Betanephthalensulfonic acid
Benzoyl peroxide
Carbon nanotubes
CSA Camphorosillinic acid
CV Cyclic voltammetry
cm Centimeter
DI Deionized water
DBSA
EB
Dodecylbenzenesulfonic acid
Emeraldine base
EDX
EIS
Energy dispersive x-ray spectroscopy
Electrochemical Impedance Spectroscopy
ES
FTIR
Emeraldine salt
Fourier transformed infrared spectroscopy
g Gram
g/mol Gram per mole
xvi
kV Kilo volt
LE Leucoemeraldine
L mol-1 cm-1 Liter per mol per centimeter
mg Milligram
mgL-1 Milligram per milliliter
mgL-1 Milligram per liter
mL Milliliter
MS Mass spectrometry
min Minute
M Molarity
molL-1 Mole per liter
mm Millimeter
mV Milli volt
mmolL-1 Milli mole per liter
µM Micromolar
µgL-1 Microgram per liter
µm Micrometer
µg cm-2
NEXAFS
NDR
Microgram per centimeter squareNear edge x-ray absorption fine structurespectroscopy
Negative differential resistance
nm Nanometer
PAA Polyacrylic acid
PANI
PANI-CSA/Au
Polyaniline
Polyaniline-camphorosillinic acid/gold
PANI/Cu Polyaniline/copper
xvii
PANI/Cu/PVA
PANI-p-TSA/Au
Polyaniline/Copper/Polyvinylalcohol
Polyaniline-paratoluenesulfonic acid-gold
PANI/PVA
PN
PPY
PSSA
Polyaniline/Polyvinylalcohol
Pernigraniline
Polypyrrole
Polystyrene sulfonic acid
PTSA
PVA
Paratoluenesulfonic acid
Polyvinyl alcohol
RP Reversed Phase
S cm-1 Siemens per centimeter
SDS Sodium dodecyl sulfate
SSNMR Solid state nuclear magnetic resonancespectroscopy
TGA Thermo gravimetric analysis
TEM Transmission electron microscopy
UV/ Vis Ultra violet visible spectroscopy
V Volt
XPS
XRD
X-ray photoelectron spectroscopy
X-ray diffraction spectroscopy
xviii
List of Publications
1. Rizwan Ullah, Graham A. Bowmaker, Khurshid Ali, Anwar-Ul-Haq Ali Shah*, Jadranka
Travas-Sejdic. Synthesis and Characterization of Polyaniline by Using Weak Oxidizing
Agent. Macromolecular symposia 2014, 339, 84-90.
2. Rizwan Ullah, Khurshid Ali, Salma Bilal, Anwar-ul-Haq Ali Shah*. Synthesis and
Characterization of Polyaniline Doped with Cu II Chloride by Inverse Emulsion
Polymerization. Synthetic metals 198 (2014) 113-117.
3. Rizwan Ullah, Graham A. Bowmaker*, Cosmin Laslau, Geoffrey I.N. Waterhouse, Zoran
D. Zujovic, Khurshid Ali, Anwar-Ul-Haq Ali Shah, Jadranka Travas-Sejdic. Synthesis of
Polyaniline by using CuCl2 as Oxidizing Agent. Synthetic Metals (Article in press)
4. Rizwan Ullah, Khurshid Ali, Muhammad Sadiq Afridi, Anwar-ul-Haq Ali Shah*. Synthesis
and characterization of leucoemeraldine form of Polyaniline by using weak oxidizing agent.
Polymer (Under review).
5. Rizwan Ullah, Khurshid Ali, Salma Bilal, Anwar-ul-Haq Ali Shah*. Synthesis and
Characterization of Polyaniline Doped with Polyvinylalcohol by Inverse Emulsion
Polymerization (To be submitted to Synthetic metals).
6. Rizwan Ullah, Khurshid Ali, Salma Bilal, Anwar-ul-Haq Ali Shah*. Synthesis and
Characterization of Polyaniline Co-Doped with Polyvinylalcohol and Cu II Chloride by
Inverse Emulsion Polymerization (In preparation to Synthetic metals).
xix
ABSTRACT
The synthesis of polyaniline (PANI) and its composites with transition metals like Cu and
polyvinyl alcohol (PVA) was carried out by the chemical oxidative polymerization and inverse
emulsion polymerization method of aniline. The samples were characterized by UV/Vis, FT-IR,
XPS, NEXAFS, and SSNMR. Elemental analysis was carried out to calculate the composition
of products. SEM images were taken to study the morphology of PANI and its composites. TGA
and XRD data was collected to study the thermal properties and crystallinity of the resulting
PANI and its composites. Cyclic voltammetry and conductivity measurement were carried out to
check the electro activity and conductivity of PANI and its composites. The UV/Vis, FT-IR,
XPS, NEXAFS and SSNMR and elemental analysis showed that polyaniline was formed in a
partially oxidized form, partially protonated, and doped with [CuCl3]- as the counter ion. Low
concentration of weak oxidant results in the formation of leucoemeraldine form of PANI. SEM
results show the spherical morphology of PANI particles doped with [CuCl3]-.
In case of co-composites of PANI with PVA and copper a smooth morphology was observed
from the SEM images as compared to the irregular morphology of PANI-PVA and PANI-Cu
obtained by inverse emulsion polymerization. The XRD and TGA confirm the amorphous nature
and an improved thermal stability of composites. CV analysis shows that PANI and its
composites are electroactive. The composites of PANI have better conductivity in comparison to
PANI as shown by conductivity measurement.
1
1. INTRODUCTION
1. Introduction
A conducting polymer is a system which possesses π-conjugated electrons for the
transport of electric current. Generally, the traditional polymers are considered to be insulators
and used in the electronic industries due to the insulating properties, whereas the conducting
polymers are semiconductors and have the ability to be doped to show metal like conductivity.
The use of conducting polymer gained tremendous importance soon after the discovery of
polyacetylene by Shirakawa [1] in 1975. A large variety of the conducting polymers are
available as a result of tremendous amount of research efforts in the field of conducting
polymers. Among the most promising types of conducting polymers, discovered by scientists,
polypyrrole, polyethylene, polythiophenes, polyphenylenevinylene, and polyaniline etc are worth
mentioning [2]. Since these materials showed some metallic properties so they were also named
as “synthetic metals”[3]. This new class of organic polymers shows important properties like low
density, resistance to corrosion, good environmental stability, high conductivity and low cost of
synthesis. The conducting polymers have a metal like optical and electrical properties,
mechanical flexibility with ease of processing, leading to the discovery of new innovative
devices and applications in the field of conducting polymers [4, 5]. The tuning of morphology of
the conducting polymers to the nanoscale by designing their dimensions often gives new
properties [6]. Examples of such properties are increased strength, greater conductivity,
molecular ordering and improved reactivity due to the large surface area [7, 8]. Conducting
polymers in combination with inorganic nanoparticles of variable size and shape give rise to new
composite materials with different physical and chemical properties thereby generating
possibilities for fascinating applications [9]. Conducting polymer blends are also studied in
2
recent years because of their significant importance in basic and applied sciences. Many devices
can be designed due to the fusion of interesting electronic, mechanical and optical properties
[10]. Conducting polymers in general are insoluble in common solvents and are infusible in
nature, thus the conventional blending techniques are not suitable for the formation of
nanocomposites, therefore, synthetic methods and techniques are to be designed to incorporate
the inorganic component into the conducting polymers. Unlike the conventional nanocomposites
where the flexibility and improved processibility for the system is provided by the polymer, the
inorganic nanoparticles are responsible for the processibility of conducting polymers [11].
1.1 Literature review
The optical, electrochemical, and electronic properties of polyaniline (PANI) drew the
attention of scientists to investigate this polymer for further applications. Moreover, the use of
PANI in light emitting diodes, electro-optics, light-weight batteries, sensors, anti-corrosion
coatings, bio capacitors and electromagnetic shielding materials has given commercial
importance to PANI [12-15]. In recent years PANI nanocomposites are gaining importance due
to new practical applications [16].
Sejdic et al. [17] successfully synthesize Polyaniline-paratoluenesufonicacid/gold (PANI-
p-TSA/Au) composite by using gold chloride trihydrate as an oxidizing agent. For the purpose of
comparison they also prepared samples by using ammoniumpersulfate (APS) as an oxidizing
agent. The samples were characterized by using SEM, TEM, FTIR, XRD, XPS and Raman
spectroscopy. The SEM images showed the spherical morphology of the composites rather than
the fibrous as in the case of APS as an oxidant. One of the reasons for the spherical morphology
reported in this work is the lower oxidation potential of gold chloride (0.994 V) as compared to
3
APS (2.0 V) due to which the kinetics of the reaction is slower thereby preventing the elongation
of chain. The second reason is the formation of elemental gold during the course of reaction
which hinders the elongation process of nanosphers to nanotubes. The TEM and XRD studies
confirmed the presence of Au particles decorated on the spheres. Significant changes were
observed in the FTIR and Raman spectra of the composites prepared by using APS and gold
chloride as oxidizing agents. The conductivity of PANI-p-TSA/Au composite is higher than the
PANI-p-TSA nanofibers at room temperature.
Wan et al. [18] prepared PANI fibers by replacing APS with FeCl3 as an oxidizing agent
in the presence of p-TSA, betanephthalensulfonic acid (β-NSA) and camphorosillinic acid
(CSA). For the purpose of comparison they also prepared samples by using APS as oxidizing
agent and found that the PANI doped with CSA, p-TSA and β-NSA in the presence of FeCl3 as
oxidizing agent have smaller diameter(10-30 nm), more conducting and has high crystallinity
than those prepared in the presence of APS. They concluded that FeCl3 is an ideal oxidant to
prepare nanoscale PANI fibers by the template free method.
Polyaniline/gold composites were chemically synthesized by Hatchett [19] and his co-
workers using tetrachloroaurate as oxidizing agent and reported large yield of reaction. They
carried out the in-situ UV/Vis spectroscopy and reported that gold colloids and short chains are
formed with a faster rate as compared to the long chain PANI. A polymer/metal composite is
formed as a result of metal encapsulation by the polymer. The resulting composites of PANI/Au
were characterized by using FTIR, XPS, and TEM. The results obtained from FTIR for PANI
were in agreement with the preparation of PANI in the presence of ammoniumpersulfate (APS).
Polycrystalline gold particles were shown by XPS and TEM with a diameter of 0.8-1 µm. From
4
the conductivity measurements they concluded that no significant change in the conductance
occurs by the encapsulation of Au in the composite.
Bertino et al. [20] synthesized the polyaniline-metal nano composite by passing γ
radiations from the aqueous solution of aniline containing a metal salt like silver nitrate and gold
chloride. The main advantage of this method is that it does not require large amounts of organic
solvents and the morphology of polyethylene fibers does not change with the addition of water
soluble salt in the aqueous solution of aniline. The synthesized nanocomposites were subjected to
TEM analysis which shows that the polyaniline fibers have a diameter of 50-100 nm. The length
of fiber varies from 1-3 µm. The metal particles were decorated on the fibers. The particle size of
metal increases with an increase in concentration of metal with respect to aniline concentration.
Several micrometers long dendritic structures were obtained when the concentration ratios of
aniline to metal is close to 1:1. The reports from XRD also confirm the presence of metal
particles by showing sharp peaks at (111), (200), (220), and (310) Bragg reflection of gold and
silver. The FTIR spectra show the characteristic peaks of benzenoid and quinoid rings of
polyaniline at 1490 cm-1 and 1570 cm-1 respectively. In the same study they concluded that
benzoyl peroxide (BPO) is a good oxidizing agent as compared to ammoniumpersulfate because
the purity of the final product is highly affected by the oxidizing agent. In case of BPO the by-
products were removed easily as compared to ammoniumpersulfate (APS).
The polyaniline/gold composites were synthesized in the presence of camphorsulfonic
acid (CSA) and hydrochloric acid (HCl) as dopant by Zhu et al. [21]. They prepared PANI doped
with HCl, PANI doped with CSA, PANI-HCl/Au composite and PANI-CSA/Au composite.
These samples were characterized by FTIR, UV/Vis and TGA to find out the incorporation of
Au. The structural morphology was examined by SEM, TEM and XRD techniques. The PANI-
5
CSA/Au composite have tubular morphology with a diameter ranging from 170-300 nm. On the
walls of the nano tubes Au particles appear as dark spots. The SEM image shows the overlap of
fibers and having a net like structure confirming that the morphology is predominantly nano
fibrous. From the XRD data they reported that HCl-doped PANI is amorphous and CSA-doped
PANI is comparatively more crystalline than HCl-doped PANI which is attributed to the
different molecular sizes. Due to the incorporation of gold in the PANI-HCl and PANI-CSA
composites new peaks appear in the XRD confirming the crystallinity of composites. In the FTIR
spectra a reasonable shift in peaks to the lower wavelength is observed due to presence of Au in
the composites. The reported reason is that Au is electron donating, which further delocalizes the
electron density of PANI. The TGA data confirm the incorporation of greater amount of Au in
PANI-CSA/Au composite as compared to PANI-HCl/Au composite which may be attributed to
the adsorption interaction of Au and CSA. From the conductivity measurements they concluded
that PANI-CSA/Au composites have more conductivity than PANI and PANI-HCl/Au
composite. Three reasons for greater conductivity of PANI-CSA/Au composite are reported.
First is the greater content of Au, second the more crystalline and third is the increase in doping
level of PANI-CSA/Au composite. The three reasons were supported by TGA, XRD and UV/Vis
spectroscopy.
Wang et al. [22] has carried out one-step synthesis of polyaniline/gold core shell
particles. They reported the use of chlorauric acid as an oxidizing agent in acidic media of acetic
acid and tween 40. The reactions were carried out at room temperature. The samples were
characterized by UV/Vis, SEM, TEM, and XRD. The SEM results show that the gold particles
are covered by the polymer layer. The XRD results confirmed the presence of gold particles in
the core shell. In the presence of acetic acid different sized PANI micro rods are formed but
6
when acetic acid was replaced by distilled water then only PANI-Au composites were formed.
From this result they concluded that acetic acid is good solvent as compared to distilled water for
the solubility of both aniline and tween 40. TEM results show the formation of micelles. This
study reveals that acetic acid is a good solvent and tween 40 is a good surfactant for the
solubility of aniline.
Wei et al. [9] proposed a one-step process for the electrochemical fabrication of an air-
stable memory device based on PANI and gold particles. They synthesized the composite
material by cyclic voltammetry at room temperature. The gold particles were found to be
distributed in the PANI matrix. The resulting composite shows that the negative differential
resistance (NDR) was repeatable even after 8 weeks exposure to air thus pave the way to use the
material in printable electronics.
Periodic acid H5IO6 was used by Muzaffer Can et al. [23] as an oxidant for the chemical
polymerization of aniline in anhydrous medium. For the chemical synthesis of conducting
polymer this is the first time that H5IO6 has been used. For the characterization of product they
used UV-Visible, FTIR spectroscopy, scanning electron microscopy (SEM), thermo gravimetric
analysis (TGA), energy dispersive x-ray (EDX) spectroscopy and electrical conductivity
measurements. The results obtained from EDX and thermo gravimetric analysis indicated the
presence of ClO-4 and iodine or iodide ion as dopant. The doping of aniline by I2 was preceded
by oxidation with IO-3 produced from H5IO6. In this work there is no residual contamination of
oxidant. In this study the extrinsic dopant I2 was produced intrinsically from H5IO6 after the
formation of IO-3. Thus for the chemical polymerization of aniline, H5IO6 was found to be a very
useful oxidative agent.
7
The amperometric detection of organophosphate was studied by Du et al. [24]. They
designed an acetyl cholinesterase biosensor in which the carbon nanotubes (CNTs) are
encapsulated into the copolymer of PANI and polypyrrole. The resulting composite was
characterized by FTIR and SEM. The electrochemical behavior was studied with the help of
electrochemical impedance spectroscopy (EIS). The biosensor being small in size shows
excellent sensitivity, high selectivity, good long-term stability, fast response, good
reproducibility and low cost of synthesis. This has opened the way to analyze the pesticides and
characterize the enzyme inhibitor by an environmental friendly tool as it does not involve the use
of any toxic agent.
The anticorrosive properties of pure PANI and its nanocomposites with clinoptilolite
(zeolite mineral) were investigated by Olad et al. [16]. The PANI samples were synthesized by
common oxidation process. The clinoptilolite were prepared from its grinded rocks in 1M HCl
solution. The PANI-clinoptilolite composites were synthesized by the chemical oxidation
method with 1%, 3% and 5% clinoptilolite by weight. The resulting composites were
characterized by FTIR, XRD and SEM. The cyclic voltamograms were recorded in 1 M H2SO4,
1 M HCl, and 1 M NaCl. The results show that the corrosion current of 3% PANI-Clinoptilolite
is less than that of pure PANI and PANI-Clinoptilolite containing 1% and 5% clinoptilolite.
Li et al. [25] prepared PANI doped with different concentrations of hydrochloric acid.
The samples were characterized by SEM, FTIR, XRD and TGA. They proposed that the
conductivity and thermoelectric properties of PANI first increase and then decrease as a function
of hydrochloric acid concentration.
8
The doping of polymeric acids like polystyrene sulfonic acid (PSSA), polyacrylic acid
(PAA) and poly methyl vinyl ether-alt-maleic acid (PMVEA) on polyaniline was carried out by
Zhang et al. [26] in the presence of ammonium persulfate as oxidizing agent and reported that
the structural morphology and size of resulting composite is greatly affected by the molecular
structure of polymeric acid. The samples were characterized by SEM, FTIR and electron
paramagnetic resonance (EPR) spectroscopy. They concluded that the outer diameter of PANI-
PSSA is larger as compared to PANI-PAA and PANI-PMVEA. The larger diameter is attributed
to the presence of a bulky benzene ring and sulphonic acid group. They further concluded that
the presence of polymeric acid on the PANI provides more sites for other functional groups to be
attached for making sensing devices.
Nuraje et al. [27] synthesized single crystalline nano needles of polypyrrole (PPY) and
polyaniline (PANI) by using interfacial polymerization. The TEM images show the rice like
structures of PANI with dimensions of 63nm×12nm and PPY of dimensions 70nm×20nm. The
needles were shown to be crystalline and conductive. The degree of crystallization can be
increased by the increase in crystallization time at the interface. This method has the advantage
of making single crystalline nano crystals while the other interfacial polymerization methods
lead to non-crystalline polymer fibers.
Gupta and co-workers [5] prepared polyaniline-silver nanocomposites to study their
optical and electrical transport properties. The samples were synthesized by the chemical
oxidation polymerization method by using ammoniumperoxidisulfate as an oxidizing agent in
the presence of negatively charged silver nanoparticles. The samples were characterized by
SEM, TEM, TGA, XRD, and FTIR etc. From the SEM and TEM analysis it appears that the
polymer matrix has metal particles dispersed in it. The XRD shows the crystalline nature of the
9
PANI-Ag nanocomposites. The thermal stability of the composite material is greater as
compared to PANI. The electrical conductivity of the composites increases with increase in
concentration of metal. The photoluminescence of the composite material is greater in
comparison to PANI.
In another study Gupta et al. [28] synthesized the composite of polyaniline nano-rods
with copper chloride. The chemical oxidation polymerization was carried out by using
ammonium persulfate as oxidizing agent. The SEM images show rod like structures. The average
diameter of the nano rods was found to be 80 nm and length of about 2-3 µm. The XRD pattern
shows that the composite material has monoclinic structure. FTIR spectra suggest that the
incorporation of copper chloride reduces the peak height and also shifts the peak position
towards the lower wavelength. This indicates the interaction of copper chloride with amine and
imine sites of the polymer. From the TGA data they concluded that the composite of PANI-
copper chloride is thermally more stable than pure polyaniline. The conductivity of the
composite has a significant increase due to the incorporation of copper chloride. This increase in
conductivity is attributed to the presence of Cu which causes an increase of metallic island.
The humidity sensing ability of polyaniline composite with polyvinyl alcohol (PVA) was
investigated by Li et al. [29]. They used polystyrenesulfonic acid (PSSA) as a template to
prepare water soluble polyaniline by the oxidation of aniline in the presence of ammonium
persulfate as an oxidant. The resulting PSSA doped PANI was dissolved in water and PVA were
refluxed into the solution. The mixture was stirred overnight to ensure complete mixing. The
PANI-PSSA and PSSA doped PANI-PVA composites were characterized by UV/Vis, FTIR, and
TEM. The humidity sensing ability of PSSA doped PANI-PVA composite is higher than the pure
PANI and PANI-PSSA.
10
PANI-PVA conducting composites were investigated by Gangopadhyay et al. [30]. An
aqueous solution stabilized by PVA was used to synthesize HCl doped PANI in the presence of
ammonium persulfate (APS) as an oxidant. The composites were characterized by UV/Vis,
SEM, TEM, and TGA. The degree of polymerization of aniline in the presence of PVA is
reported to be decreasing due to the steric stabilization of PVA. They added that the dispersion
shows the conductivity of PANI and mechanical strength of PVA. The composite isolated from
the dispersion was subjected to TEM analysis which shows the presence of PANI spheres in the
network of PVA contrary to the rice-grain morphology or needle like morphology. From TGA
they concluded an appreciable increase in thermal stability of the composite.
J. Bhadra and Sarkar [10] synthesized a composite film of PANI-PVA to study its electrical
and optical properties. The SEM results show the presence of polyaniline grains on the PVA
matrix. The size of grains ranges from 0.3 to 1.2 µm. They reported that spherical and rod
shaped nanoparticles are formed at higher concentration of PVA. The amorphous nature of
composite was shown by XRD. They reported PANI-PVA cross linking from the FTIR spectra.
The decrease in conductivity is observed as PVA concentration increases in the composite.
1.2 Polyaniline
Polyaniline (PANI) formerly known as “aniline black” is deposited over the anode during the
electrolysis of aniline. Among the conducting polymers polyaniline (PANI) has got much more
attention due to its unique properties, like cost-effective monomers, high yield of reaction and
excellent stability [31]. PANI has got many industrial applications like resistance to corrosion in
paint industry, removal of mercury from water, light emitting diodes, surgical instruments, light-
weight batteries and solar cells [32-34].
11
1.2.1 Structure of Polyaniline
A linear octameric structure of PANI was proposed by Woodhead and Green [35, 36] for
the first time. According to them the aromatic aniline molecules are arranged head to tail at the
para position forming a linear chain. In PANI the flexible –NH- group is attached to the
phenylene group on either side. The presence of –NH- group is responsible for the physical and
chemical properties of PANI along with protonation and deprotonation process [37]. There are
three different oxidation states of PANI i.e. fully oxidized pernigraniline (PN), fully reduced
leucoemeraldine (LE), and half oxidized emeraldine base (EB) as shown in Figure 1.1. The
reason for the different oxidation states is due to the difference in the number of imine and amine
units in PANI. Among the three forms only the emeraldine salt (ES) is conductive which is
obtained by protonation of emeraldine base.
* N N N nN
Pernigraniline (Violet and insulator)
* NH NH NH NHn
Leucoemeraldine (Pale yellow and insulator)
12
* NH NH Nn
N
Emeraldine base (Blue and insulator)
* NH NH NHn
NH
Emeraldine salt (Green and conductive)
Figure 1.1 Various redox states of PANI.
1.2.2 Conductivity of polyaniline (PANI)
The existence of PANI in three different oxidation states (pernigraniline, leucoemeraldine
and emeraldine form) leads to the difference in physicochemical properties [13, 38, 39]. The
emeraldine base form of PANI is protonated to emeraldine salt form which has conductivity in
the range of semiconductors 100 S cm-1. The conductivity of emeraldine salt is more than that of
pure polymers (<10-9 S cm-1) while less than that of typical metal (>104 S cm-1). The emeraldine
salt can be converted back to emeraldine base by treatment with alkaline solution. The
interconversion of emeraldine base and emeraldine salt is shown in Figure 1.2 [39].
13
* NH NH Nn
N
+2nH A-2nH A
* NH NH NHn
NHAA
Figure 1.2. Interconversion of emeraldine base and emeraldine salt.
Depending on the doping of PANI the conductivity can be changed to a wide range (<10-12 to
~105 S cm-1) [40]. The physical and chemical properties of PANI change in response to the
various external inducements thereby providing the space to use the PANI material for various
applications, e.g., memory devices, catalysis and chemical sensors [41]. Other uses like electro
chromic devices, microelectronics, plastic development etc. are attributed to the combination of
electrical and material properties of PANI.
1.2.3 Mechanism of Conductivity
The variable electrical conductivity of polymers is attributed to doping. Extensive
research work has been conducted to investigate the transportation of charge in these polymers
but the phenomenon is still poorly understood [40]. The main reason for the transportation of
charge in conducting polymers is conjugation among the unsaturated carbon atoms. New type of
charge transfer phenomenon is observed in the conjugated polymers due to the existence of
localized electronic energy states less than the band gap arising due to changes in local bond
order [40]. During polymerization reactions topological defects are introduced into the
14
conducting polymers with non-degenerate ground states. The energy of the radical cation
generated by the removal of charge from the valence band lies in the band gap. when radical
cation is partly delocalized over some polymer fragments, it is called small polaron in solid state
physics terms. The polaron formation is responsible for two localized electronic states in the
band and structural deformation of the lattice. Brazovski and Kirova [42] proposed a model of
three optical transitions due to the formation of polaron.
The removal of the second electron from the system creates another polaron when an
electron is removed from another segment of the polymer or from the already existing polaron to
create a bipolaron. A bipolaron also causes structural deformation while the two charges act as a
single pair. The polaron and bipolaron become mobile in response to the external electric field
via the rearrangement of conjugation.
The increase in conductivity of PANI is attributed to the charged species generated
during the protonation of polymer [43]. Other mechanisms of conductivity of PANI include
temperature based one-dimensional variable range hopping or three-dimensional fluctuation-
induced tunneling models [44].
1.2.4 Synthesis of Polyaniline
Generally, the synthesis of polyaniline is carried out by two methods i.e. chemical
oxidative polymerization and electrochemical polymerization [12]. The chemical method of
polymerization involves the direct oxidation of aniline to polyaniline by the use of oxidizing
agents, like ammonium persulfate, hydrogen peroxide, potassium dichromate, potassium iodate
etc., in an acidic media at pH range between 0 and 2 [38]. However, neutral and basic media are
also reported for the chemical synthesis of polyaniline at a pH range of 9-10 [38]. High
15
molecular weight PANI can be obtained at low temperature ranging from -15 to 5 0C. The
chemical synthesis of PANI results in bulk quantity of product with ease of processibility.
However, the higher Ionic strength of the medium and the excess of the oxidant lead to the
formation of essentially inflexible material which is one of the disadvantages of chemical
method.
Other chemical methods include interfacial polymerization, emulsion polymerization, and
dispersion polymerization etc. A list of oxidants and polymerization routes are given in the
literature [38, 40].
The synthesis of PANI by electrochemical method involves the anodic oxidation of aniline on an
inert metallic electrode usually platinum using potentiostatic or galvanostatic mode. Other
electrode materials used are copper, lead, iron, and zinc [38]. In potentiostatic mode the potential
is fixed (ESCE= 0.7-1V) or cycled in a range of -0.2 to 0.7-1.2V. An inert atmosphere is provided
to carry out the anodic oxidation at ambient temperature. PANI synthesized by potential cycling
is more homogeneous [38]. The advantage of electrochemical method is the easy formation a
thin or thick coating for conceivable applications.
1.2.5 Mechanisms of polymerization
The nature and physicochemical properties of PANI, synthesized by a variety of methods,
differ up to a large extent. In order to identify the formation of intermediates and steps involved
in the synthesis of PANI various kinetic studies and mechanisms are proposed. The study of
these reaction mechanisms is of prime importance to correlate the properties of polymeric
material to the possible reaction routes [45]. In order to find out the mechanism for the synthesis
16
of PANI various chemical and electrochemical methods have been proposed by different
scientists which are reviewed in the literature [38].
The mechanism for PANI formation is supposed to be a self-catalyzing reaction which
obeys the law Kc= ∆i/n FA. Where n is the number of electron transferred, A is the electrode
area, F is faraday’s constant, and ∆i is the change in current. The value of Kc (Autocatalytic rate
constant) is ~0.47 s-1 when the thickness of PANI film is 140 nm [46]. The formation of a
radical cation is considered to be the first step in the mechanism for synthesis of PANI. The
radical cation is resonance stabilized as shown in Fig. 1.3.
NH2 NHH
. NHH
H.N
HH
.
H
NHH
.H
e-
Figure 1.3. Radical cation formation and its resonance stabilization.
According to Mohilner et al. [47] the oxidation of aniline in an acidic medium of sulfuric
acid ( pH 2-5) is a progression of fast electrochemical-chemical-electrochemical (ECE)
reactions, resulting in para-coupled chains. However, the radical coupling at ortho position is
responsible for the low yield of reaction due to un-exclusive para-coupling [38]. The first
reaction intermediate can react with a free monomer or undergo further oxidation. According to
Yang and Bard [48] in the early stages of PANI polymerization, the dimer of aniline (p-
aminodiphenylamin) is predominantly produced with another minor intermediate benzidine.(
Fig. 1.4)
17
NH
H
HNH
H
HHNH .
H
H
N
H
HNH
H
HH
N N
H
H
+
-2H
2 ..
H
Figure 1.4. Conversion of radical cation to para-aminodiphenylamine.
In the next step the para-aminodiphenylamine rapidly undergoes further polymerization resulting
in the formation of tetramer followed by octamer and ultimately results into emeraldine [47].
Since less positive potential is required for the electro-oxidation of oligomers as compared to
aniline monomer, therefore, the mechanism of aniline polymerization is proposed to be
autocatalytic which is observed in aqueous medium of considerable acidity [45].
1.2.6 Doping of PANI
The doping is achieved by the increase or decrease in the number of electrons associated
with the polymer due to the partial oxidation or reduction of π conjugated system of polymer
[40]. An appreciable change in electronic transport properties is observed when PANI is doped
with anions either chemically or electrochemically [49]. Among the oxidation states of PANI the
emeraldine form is susceptible to pH resulting in emeraldine base (EB) and emeraldine salt (ES).
The non-conducting EB can be converted into the conducting ES form without changing the total
number of electrons [50]. This can be achieved by the addition of mineral or organic acid to
protonate the –NH group of EB form of PANI. The addition of acid is called acid doping.
18
* N N N nN
* NH NH NHn
NHAA
+2nH A-2nH A
Figure 1.5. Acid doping of PANI.
The conductivity of acid doped PANI is more than eight orders of magnitude larger than the
undoped form [49]. During the process of protonation the accumulated positive charges on the
polymer backbone are neutralized by the counter (negatively charged) ions of the dopant.
Significant changes in the crystallinity, electronic structure, and solubility etc. are associated
with protonation [40]. The change in pH of dopant solution provides the way to control the
conductivity and degree of protonation by acid. The most commonly used dopants are mineral
acids like H2SO4 and HCl.
1.3 Characterization of PANI
The various physicochemical techniques used for the characterization of polyaniline
synthesized by chemical or electrochemical method are discussed below.
1.3.1 UV/Visible spectroscopy
UV/Visible spectroscopy is one of the most important characterization techniques for
PANI due to the various oxidation states of PANI with different colors. It is a useful tool to trace
the color changes associated with the sensitivity of PANI to pH changes. The qualitative
information about the degree of conjugation, level of doping and the existence of radical cation
19
in the polymer can be achieved by the electronic absorption spectra of PANI dissolved in
suitable solvent or electrochemically deposited over an electrode in the form of film. Clear
monitoring of the change from conductor to insulator with respect to change in pH of the
medium can be carried with ease. In order to understand the interconversion of different
oxidation states of PANI; in situ UV/Vis spectroscopy in combination with applied potential is
very useful. The change in electrical conductivity of different oxidation states can be correlated
with the change in absorbance values. The interaction between PANI and the molecules of
solvent used to dissolve PANI can also be studied by this method. The kinetics studies of aniline
polymerization can also be traced by the electronic absorption spectroscopy [45].
1.3.2 FTIR spectroscopy
The Fourier Transform Infrared (FTIR) spectroscopy is a non-destructive, faster, more
sensitive and widely used technique for the characterization of solids, liquids, gases, and film
samples in laboratory and industry. It is a powerful technique available to the chemists to find
out the structure of molecule present in the sample. The technique also finds its applications in
characterizing the intermediate products during the course of reactions. In case of PANI
characterization important information about the presence of bands for both amine and imine
groups can be gained which will determine the oxidation state of PANI products. The presence
of many functional groups on the polymer backbone can be deduced from the corresponding
bands in the FTIR spectrum. The doping and dedoping of PANI can also be studied from the
vibrational spectroscopy. The vibrational spectroscopic tool has many industrial applications in
characterizing samples related to biomedical research, foodstuff, polymerization products etc.
The vibrational spectroscopic technique is fast, has ease of calibration, more sensitivity,
excellent specificity and applicability in both quantitative and qualitative analysis.
20
1.3.3 X-ray diffraction (XRD)
X-ray diffraction is a non-destructive and unique technique to identify the crystallinity
and analyze the structural properties like crystal orientation, grain size, stress, defects and phase
composition by bombardment of the solid samples from different angles. The crystal lattice of
the sample diffract the X-ray from its various planes according to Bragg’s equation nλ=2dsinθ
where n is an integer, λ is the wavelength of X-ray, d is lattice planes distance and θ is the angle
of diffraction.
Figure 1.6. X-rays diffraction in a crystalline material.
A diffraction pattern emerges by the variation of the angle of incidence which is the
characteristic of the sample. The resultant X-ray pattern, along with peak positions, width,
intensities and shape, provides significant information about the possible structure of the
material. The X-ray diffraction of PANI will not show sharp peaks indicating the amorphous
nature of PANI which is the characteristics of polymers. However, at 2θ ranging from 20⁰-26⁰ a
21
diffused broad peak is displayed by the polymer samples. Insertion of metal will cause a change
in the XRD pattern of the polymer and corresponding change in the intensity, width and position
of the peak thereby causing an increase in the conductivity due to the increase in d-space [51].
1.3.4 Cyclic voltammetry
Cyclic voltammetry is a powerful, most widely used and efficient electrochemical
technique to acquire information about the inter conversion of various oxidation states of PANI.
Besides characterization, the technique also finds its applications in the synthesis of PANI.
Considerable information about the kinetics and thermodynamics of oxidation-reduction
reactions can readily be deduced from the cyclic voltammetry. The electrochemical responses of
various oxidations states of PANI results in the appearance of peaks at various positions in the
cyclic voltamogram (plot of current verses potential). The interconversion of any two oxidation
states of PANI along with the injection of charge can be studied from the peaks in the cyclic
voltamogram. Cyclic voltammetry also provides important information about the effect of
supporting electrolyte on the morphology and conductivity of PANI during the process of
polymerization.
1.3.5 Scanning electron microscopy (SEM)
The physicochemical properties of powder PANI, synthesized chemically, or PANI films,
synthesized electrochemically, are highly influenced by the morphology of polymer [38]. The
morphology of PANI is generally investigated by scanning electron microscopy (SEM). The
micro and nano structures of PANI can be studied at a high magnification. Various
physicochemical properties like crystallinity, mechanical strength, electrical conductivity etc. can
be related to the surface morphology obtained from SEM images.
22
1.3.6 Elemental analysis
Elemental analysis is one of the basic characterization techniques used in synthetic
chemistry to find out the composition of sample material. The stoichiometry of sample material
can be calculated from the percent weight of carbon, hydrogen, nitrogen and sulfur which are
provided by the elemental analysis. Moreover, the ratio of carbon to hydrogen and carbon to
nitrogen can also be calculated from the elemental analysis. The degree of doping can also be
calculated from the elemental analysis for example, when transition metal salts of Fe (III), and
Cu (II) are used as dopant in PANI chains, the imine site co-ordinates with the metal cation
resulting in the 85% and 50% doping of PANI by iron and copper ion respectively [52].
Important information about deducing the structure and molecular weight of the sample material
are provided by elemental analysis. In case of PANI the C/N ratio and H/C ratio is useful in the
determination of the oxidation state of PANI.
1.4 Solubility of PANI
The solubility of polyaniline is of high interest regarding its scientific and commercial
applications. Scientifically the elucidation of molecular structure and configuration from the
molecular weight obtained by the analytical data provided by solubility of PANI is of prime
importance. Commercially many technological devices can be designed by the soluble PANI [3].
The conducting polymers are mostly insoluble in their doped state [53]. The poor
processibility of conducting emeraldine salt form of PANI is attributed to its non solubility in
common organic solvents [54]. According to Heeger [31] the discovery of PANI paved the way
to overcome the problem of processibility of conducting polymers. However, the poor solubility
of high molecular weight PANI is a barrier in making useful devices and objects. The instability
23
of PANI at melt process temperature has blocked the way of processing it like conventional
thermoplastics polymers [55]. The fundamental thermodynamic properties like unfavorable
entropy of dissolution, unmoldability and high lattice energy of PANI has high influence on the
solubility of PANI [56]. Another reason for the poor solubility of PANI is the non availability of
such solvents which could simultaneously dissolve both the hydrophobic and hydrophilic part of
the polymer. In order to improve upon the solubility and processibility of PANI many attempts
has been made by scientists from all over the world [57]. The use of substituted aniline as
monomer, copolymerization of aniline, blending of PANI with other polymers, doping with
anionic surfactants and formation of PANI composites are being extensively studied. A brief
discussion of the above mentioned methodologies is given below.
1.5 Polymerization of substituted aniline
The use of substituted aniline for polymerization to improve upon the solubility of PANI
is one of the most recently studied methodologies. The substituent like alkoxy [58], alkyle [59],
phosphoric acid [60], sulfonic acid [61] groups with a solubilizing effect are chosen for the
purpose of increasing solubility of resulting polymer. In addition to increase the solubility of
PANI the thermal stability of acid doped PANI is also increased. The substituted aniline can also
be polymerized chemically [62] or electrochemically [63] just in the same way as their parent
monomer. The major problem with the polymerization of substituted aniline is the decrease in
conductivity of resulting polymer [64].
24
1.5.1 Copolymerization of aniline
In order to bring the diverse physicochemical properties of different polymers into a
single polymer structure the copolymerization technique is applied. As discussed before, that the
conductivity is greatly reduced by the polymerization of substituted aniline at the cost of
solubility but in case of copolymerization the resulting polymeric system has the conductivity
just like PANI and solubility like the polymers obtained by the polymerization of substituted
aniline [65-67].
1.5.2 PANI blends
A blend is a mixture of two or more physically mixed polymers having different chemical
composition. Several types of PANI conductive blends with an increase in processibility are
reported in literature [68, 69]. The idea of PANI blends was introduce to make it melt
processable by increasing stiffness and flexibility of PANI. The mechanical strength of the blend
decreases to a high extent as a result of phase separation between the two components [70]. High
flexibility for the material having less than 16 % PANI composition by weight has been reported
in literature [69]. The PANI salt blended with poly(vinyl chloride) [71], poly(vinyl alcohol) [72],
poly(styrene) [73] and poly(amides) [74] are being extensively studied.
1.5.3 PANI doped with surfactants
The synthesis of high molecular weight PANI is carried out by the chemical
polymerization of aniline in a micelles system which not only increases the yield of reaction but
also leads to accelerated polymerization [75]. Similarly, the presence of sodium dodecyl sulfate
(SDS) accelerates the electro-polymerization of aniline [76]. Colloidal PANI dispersion
25
synthesis is also reported in the presence of SDS as surfactant [75, 77, 78]. The dispersion of
HCl doped PANI synthesized in the presence of SDS micelle medium is reported to be stable up
to a pH =8 [75]. SDS was used as a surfactant by Hassan et al. [79] for the polymerization of
aniline and reported that the polymer size is greatly affected by both the concentration of
monomer and micelle size. In the synthesis of polymer in the presence of micelle the
polymerization reaction takes place at the interface of micelle-water system. In such system
dynamic equilibrium exist between the surfactant monomers and micelle in the solution. The
intermediate hydrophobic products obtained from the polymerization are incorporated into the
micelles because of their poor solubility in water. The SDS molecule are incorporated and
adsorbed in the polymer particles thereby stabilizing them [77].
1.5.4 Composites of PANI
In recent years researchers have shown a great deal of interest in the organic- inorganic
composites due to their potential applications in various technological processes. Among these,
PANI is of much importance due to its versatile conducting properties. The conductivity of
PANI can be tuned by doping with suitable dopants. The composites of PANI with noble metals
can be used in optical and electrical appliances and also for catalytic purposes [80]. The
reduction of silver nitrate by using emeraldine base (EB) form of PANI was carried out by
stejskal et al. [81] to synthesize PANI-silver nanocomposites. The resulting PANI-silver
nanocomposites show an increase in conductivity. PANI-gold nanocomposites were synthesized
by Gupta et al. [82] using chemical oxidative method and studied the optical and electrical
transport properties. In another study Gupta and his coworkers [5] synthesized the PANI-silver
nanocomposites and reported their electrical transport and optical properties.
26
1.6 Aims and objectives of the work
The aims of the present study are twofold: (a) To study the effect of the use of copper(II) as a
milder oxidizing agent than those normally used (ammonium persulfate, benzoylperoxide,
hydrogen peroxide, etc.) on the aniline polymerization reaction and its potential PANI product.
(b) To determine the nature of any copper incorporated in the reaction product. The latter is
particularly important in relation to the proposed use of such reactions to produce
polyaniline/metal composite materials, which are the subject of a recent review [83], but it is
evident from the literature cited above that the chemical state of the copper that has been
proposed to be incorporated in the product is quite variable [83-86]. Indeed, the formation of
PANI by the oxidation of aniline by copper(II) compounds has been called into question in
studies of reactions of aniline with CuSO4, CuCl2 and CuBr2, where 2:1 coordination adducts of
aniline with these copper(II) compounds precipitated rather than the expected PANI product
[87]. In the present work we extend the study of the CuCl2/aniline system to explore the effect of
using higher CuCl2 concentrations; previous studies have shown that the oxidation potential of
CuCl2 increases with increasing concentration [88]. A previous study [86] has proposed a
catalytic (rather than an oxidative) role for copper(II) in aniline oxidation reactions in the
presence of copper(II). The possibility that PANI might be formed catalytically by aerial
oxidation of aniline in the presence of CuCl2 has been excluded in the present study by carrying
out the reaction in the absence of air. It was found that polyaniline emeraldine base (EB-PANI)
doped with [CuCl3]- forms under these conditions. CuCl2 is a weaker oxidant than, e.g. AgNO3,
and this study further supports the view that weak oxidizing agents can be used for aniline
polymerization reaction. The reaction yield is low, but can be increased by increasing the CuCl2
concentration. The present study also focuses on the synthesis and characterization of PANI and
to make its composites with copper and polyvinylalcohol (PVA) and to investigate into the
conductivity, crystallinity, redox properties and stability of resulting composites.
***********************
27
28
2. EXPERIMENTAL
PART I
2.0 Synthesis and Characterization of Polyaniline by using CuCl2 as Oxidizingagent
2.1 Material
Aniline monomer (99.5%) was purchased from Sigma Aldrich and distilled twice before
use. p-toluene sulfonic acid (p-TSA) (synthesis grade) was purchased from Scharlau and used as
received. Anhydrous copper chloride (97%) from Sigma Aldrich was used as received.
2.2 Procedure
A 10 mL solution of (0.2 M aniline and 0.2 M p-TSA) was prepared in milli-Q water.
The pH of the solution was 4.70. This solution was placed at 5±1 0C for 10-15 minutes. 10 mL of
3 M pre-cooled copper(II) chloride solution was added dropwise to 10 mL of the aniline-p-TSA
solution under nitrogen atmosphere. The reaction mixture was left undisturbed for 24h at room
temperature under nitrogen atmosphere. The reaction mixture turned greenish black and had a
final pH of 2. The precipitate was filtered and washed several times with milli-Q water followed
by acetone. The product was dried for 24 h in a vacuum oven at room temperature and labeled as
B-PANI. Similar reactions with oxidant : monomer ratios ‘R’ from 1 to 15 were investigated by
varying the CuCl2 concentration. The B-PANI was washed with 1M HCl to remove basic
impurities and the sample was labeled as H-PANI. When the B-PANI was treated with 35%
hydrazine it was labeled as PANI (Scheme 1).
29
Scheme 1.Treatment of the B-PANI sample with various chemicals to get the products.
2.3 Dedoping of B-PANI and H-PANI
The B-PANI and H-PANI samples were dedoped with 10% NH4OH solution according
to the procedure described by Bian and Yu [89]. The dedoped PANI samples were labeled as
DB-PANI and DH-PANI (Scheme 1).
2.4 Reduction of PANI, DB-PANI and DH-PANI
The PANI, DB-PANI and DH-PANI samples were reduced by the addition of 35%
aqueous hydrazine [90] and labeled as R-PANI, RB-PANI and RH-PANI, respectively (Scheme
1).
2.5 Characterization
The yield of product was calculated for reactions with various oxidant to monomer ratios
ranging from 1 to 15. The initial and final pH of the reaction mixture was measured for these
oxidant to monomer ratios. The weight loss following the washing of the products was also
calculated.
2.5.1 FTIR Spectroscopy
A Perkin Elmer series Spectrum 400 FTIR spectrometer was used to record FTIR spectra.
The spectral region from 4000 to 400 cm-1 was selected with a resolution of 4 cm-1 for all
30
samples. The number of scans for each sample was 10 and the spectra were collected in
attenuated total reflection (ATR) mode. For the data analysis the standard software (Sigma plot
11) was used.
2.5.2 UV/Vis Spectroscopy
The UV-Vis spectra were recorded on solutions in N-methyl pyrrolidone (NMP) as
solvent using a Shimadzu UV/Vis 1700 spectrophotometer. The spectral region from 900 to 200
nm was selected with a sampling interval of 0.5 nm.
2.5.3 Elemental Analysis
Elemental analysis was carried out by the Cambell Microanalytical Laboratory at the
University of Otago, Dunedin, New Zealand.
2.5.4 X-ray Photoelectron Spectroscopy (XPS)
XPS data were collected using a Kratos Axis Ultra DLD equipped with a hemispherical
electron energy analyzer and an analysis chamber of base pressure ~1×10-9 torr. Samples were
excited using monochromatic Al Kα X-rays (1486.69eV), with the X-ray source operating at 100
W. Samples were mounted on carbon adhesive tape for analysis. A charge neutralization system
was used to alleviate sample charge build up during X-ray irradiation. Survey scans were
collected at a pass energy of 80 eV over the binding energy range 1200-0 eV, while core level
scans were collected with a pass energy of 20 eV. The spectra were calibrated against the C 1s
signal at 285 eV from adventitious hydrocarbons. Elements present in the samples were
quantified based on C 1s, N 1s, Cu 2p, Cl 2p, Si 2p and S 2p peak areas and relevant sensitivity
factors.
2.5.5 Near Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy
N K-edge NEXAFS data was recorded on the soft X-ray spectroscopy beam line of the
Australian Synchrotron. The NEXAFS data was taken in both partial electron yield (PEY) mode.
The PEY spectra were normalized to a photo-diode current measured simultaneously to cancel
any contributions originating from impurities present in the beam line which may contribute to
31
changes in the photon intensity. The measurements were carried out in high resolution (HR)
mode by increasing the photon energies in steps of 0.05 or 0.1 eV.
2.5.6 Solid-State NMR
All solid-state NMR experiments were carried out on dry powdered samples using a
Bruker AVANCE 300 spectrometer operating at 300.13 MHz proton frequency. Basic spectra
were obtained by using the standard CP MAS (Cross-Polarization Magic Angle Spinning)
technique. The experiments were carried out using a 7 mm Bruker spinning probe with zirconia
rotors. The magic angle was adjusted by maximizing the side bands of the 79Br signal of a KBr
sample. The proton 90o pulse duration was 4.2 μs and the frequency of the continuous wave
decoupling field was 62.5 kHz. The contact time was 1.5 ms. The spectral width was 40 kHz.
The 13C chemical shift scale is referenced to tetramethylsilane (TMS). The samples were rotated
at 7000 1 Hz.
2.5.7 SEM Analysis
The SEM analysis was performed in Centralized Resource Laboratories (CRL)
University of Peshawar, Pakistan by using scannining electron microscope Model JSM-5910
JEOL Japan.
PART II
2.6 Synthesis and Characterization of Leucoemeraldine
2.6.1 Materials
Aniline monomer (99.5%) was purchased from Sigma Aldrich and distilled twice before
use. para-toluene sulfonic acid (Synthesis grade) was purchased from Scharlau and used as
received. Anhydrous copper chloride (97%) from Sigma Aldrich was used as received.
2.6.2 Procedure
A 10 mL solution of (0.2 M p-TSA and 0.2 M aniline) was prepared in deionized water.
The pH of the solution was 4.80. 10 mL of this solution was placed at 5±1 0C for 15-20 minutes.
10 mL (0.01 M copper chloride) precooled solution was added to the aniline-p-TSA solution.
32
The reaction mixture was stirrered at room temperature under the nitrogen atmosphere, for 24 h.
The final pH of reaction mixture was found to be 3.7. The precipitate was centrifuged and
washed with deionized water followed by acetone to remove unreacted material. The product
obtained was dried for 24h at room temperature in a vacuum oven and labeled as L-PANI. The
oxidant: monomer ratios 0.05, 0.25, 0.50, 0.75, 1 and 1.25 were investigated by changing the
concentration of CuCl2.
2.6.3 Characterization
The amount of product was calculated for various oxidant to monomer ratios ranging
from 0.05 to 1.25. The initial and final pH of various oxidant to monomer ratios in the reaction
mixture was noted.
2.6.3.1 FTIR Spectroscopy
FTIR spectra were recorded by using Perkin Elmer spectrophotometer series 400 FTIR.
The spectra were recorded in the spectral region ranging from 4000 to 400 cm-1 with a resolution
of 4 cm-1. The spectra were collected in attenuated total reflection (ATR) mode with 10 numbers
of scans for all samples. The standard software (Sigma plot 11) was used for the data analysis.
2.6.3.2 UV/Vis Spectroscopy
A Shimadzu UV/Vis 1700 spectrophotometer was used to record the UV/Vis spectra. The
sampling interval was 0.5 nm and the spectra were recorded in spectral region ranging from 800
to 200 nm.
2.6.3.3 Elemental Analysis
Elemental analysis was performed by using Elementar CHNS Analyzer Germany at
Pakistan Council of Scientific and Industrial Research (PCSIR) Laboratory Peshawar, Pakistan.
33
PART III
2.7 Synthesis and Characterization of Polyaniline Doped with Cu II Chloride
by Inverse Emulsion Polymerization
2.7.1 Materials
Aniline monomer reagent grade was purchased from Acros organics and distilled twice
before use. Toluene (BDH), 2-propanol (Merck), benzoyl peroxide (Merck) and DBSA (Acros)
were used as received.
2.7.2 Procedure
The material was synthesized according to the procedure mentioned in literature [13]. In
a typical experiment 50 mL of toluene was taken in a 100 mL round bottom flask. 0.40 g
Benzoyl peroxide was added to it under mechanical stirring. 10 mL of 2-propanol was added to
the above solution. To the above mixture 1.5 mL DBSA, 0.2 mL aniline and 10 mL (0.6M
CuCl2) solution in deionized water was added to form a white milky emulsion. A greenish brown
color appears after 7 hours. The reaction was allowed to proceed for 24h. In the end the mixture
was transferred into a separating funnel for the separation of organic layer from the aqueous
layer. The organic layer containing polyaniline was extensively washed with acetone and the
product obtained was transferred into a petri dish and dried in oven for 24h at 40 0C. The
polymer was broken into flakes by the addition of small amount of acetone. The polymer was
separated from the petri dish and labeled as PANI-Cu. Several different concentrations of CuCl2
were investigated. For PANI sample preparation only deionized water was added to produce the
milky emulsion.
2.7.3 Characterization
The amount of product was calculated for various addition of CuCl2 solution ranging
from 0.2 to 0.7M.
2.7.3.1 Conductivity Measurements
A four point probe Jandel Model RM2 instrument was used to carry out the conductivity
measurements of the PANI-Cu composites. The powder samples were compressed to form a
34
solid pellet and four electrical contacts were made with the solid pellet to measure the
conductivity.
2.7.3.2 UV/Vis Spectroscopy
A Shimadzu UV/Vis 1700 spectrophotometer was used to record the UV/Vis spectra. The
spectra were recorded with a sampling interval of 0.5 nm in the spectral region from 900 to 200
nm.
2.7.3.3 FTIR Spectroscopy
FTIR spectra were recorded in a region ranging from 400 to 4000 cm-1 by using IR
Prestige-21 FTIR Spectrophotometer Shimadzu Japan. The number of scans for each sample was
10.
2.7.3.4 Thermo Gravimetric Analysis (TGA)
The TGA was performed on solid samples at a temperature range from 0 to 600 0C by
using Diamond TG/DTA Perkin Elmer USA in the Centralized Resource Laboratories University
of Peshawar Pakistan.
2.7.3.5 X-ray Diffraction (XRD) Analysis
The XRD analysis of solid samples was carried out by using Siemens diffractometer D
5000 at the Polymer Electronic Research Centre University of Auckland New Zealand.
2.7.3.6 Scanning Electron Microscopy
The SEM was carried out in Centralized Resource Laboratories University of Peshawar
Pakistan by using scannining electron microscope Model JSM-5910 Jeol Japan.
2.7.3.7 Cyclic Voltammetry
Cyclic voltammetry (CV) was carried out in National Centre of Excellence in Physical
Chemistry, University of Peshawar, Pakistan by using ALS/DY 2323 Biopotentiostate. A gold
coiled wire was used as counter electrode while gold foil (9.1×9.6 mm in size) and 0.27 mm
thick was used as working electrode. The calomel electrode was used as reference. On the gold
foil electrode a thin film of the polymer was deposited and the CVs were recorded with a scan
rate of 50 mV S-1 in 0.5M H2SO4 solution as supporting electrolyte.
35
PART IV
2.8 Synthesis and Characterization of Polyaniline Doped with
Polyvinylalcohol by Inverse Emulsion Polymerization
2.8.1 Materials
Reagent grade aniline monomer was purchased from Acros Organics and distilled twice
before use. DBSA (Acros), 2-propanol (Merck), benzoyl peroxide (Merck), and toluene (BDH)
were used as received.
2.8.2 Procedure
The samples were synthesized according to the procedure mentioned in literature [13]. In
a typical experiment 50 mL of toluene was taken in a 100 mL round bottom flask. 0.40 g of
benzoyl peroxide was added to it under mechanical stirring. To the above solution 10 mL of 2-
propanol was added. 1.5 mL DBSA, 0.2 mL aniline and 10 mL (1% PVA) solution, in deionized
water, was added to the above mixture to form a white milky emulsion. The reaction mixture
turns greenish brown after 7h and was allowed to proceed for 24h. The aqueous layer was
separated from the organic layer in a separating funnel. Extensive washing of the organic layer
with acetone was carried out until the unreacted material is removed and the product obtained
was transferred into a petri dish and dried in oven for 24h at 40 0C. The polymer was broken into
flakes by the addition of small amount of acetone. The polymer was separated from the petri dish
and labeled as PANI/PVA. Several different concentrations of PVA were investigated.
2.8.3 Characterization
The amount of product was calculated for various addition of CuCl2 solution ranging
from 0.2 to 0.7M.
36
2.8.3.1 Conductivity Measurements
The conductivity measurements of the PANI/PVA composites were carried out by using
four point probe Jandel Model RM2. Four electrical contacts were made with the solid pellet
compressed under high pressure of 800 bar.
2.8.3.2 UV/Vis Spectroscopy
To record the UV/Vis spectra a Shimadzu UV/Vis 1700 Spectrophotometer was used.
The spectral region from 900 to 200 nm was selected and the spectra were recorded with a
sampling interval of 0.5 nm.
2.8.3.3 FTIR Spectroscopy
FTIR spectra were recorded by using IR prestige-21 FTIR Spectrophotometer Shimadzu
Japan in a region ranging from 400 to 4000 cm-1. The spectra were collected with 10 numbers of
scans for each sample.
2.8.3.4 Thermogravimetric Analysis (TGA)
The TGA was performed on solid samples at a temperature range from 30 to 600 0C by
using Diamond TG/DTA Perkin Elmer USA in the Centralized Resource Laboratories University
of Peshawar Pakistan.
2.8.3.5 X-ray Diffraction (XRD) Measurements
The XRD of solid samples was carried out by using Siemens diffractometer D 5000 at the
Polymer Electronic Research Centre University of Auckland New Zealand.
2.8.3.6 Scanning Electron Microscopy (SEM)
The SEM was carried out in Centralized Resource Laboratories University of Peshawar
Pakistan by using scannining electron microscope Model JSM-5910 JEOL Japan.
37
2.8.3.7 Cyclic Voltammetry
Cyclic voltammetry (CV) was carried out by using ALS/DY 2323 Biopotentiostate in
National Centre of Excellence in Physical Chemistry, University of Peshawar, Pakistan. Gold
foil was used as working electrode and gold coiled wire as counter electrode. The calomel
electrode was used as reference. A thin film of the polymer was deposited on the gold electrode
and the CVs were recorded in 0.5M H2SO4 solution as supporting electrolyte. The scan rate was
50 mV S-1.
PART V
2.9 Synthesis and Characterization of Polyaniline Co-doped withPolyvinylalcohol and Cu by Inverse Emulsion Polymerization
2.9.1 Materials
The monomer aniline (reagent grade) was purchased from Acros Organics and distilled
twice before use. Dodecylbenzene sulfonic acid (DBSA) from Acros Organics, 2-propanol and
benzoyl peroxide (BPO) from Merck and toluene from BDH were used as received.
2.9.2 Procedure
The synthesis was carried out according to the procedure mentioned in [13]. In a typical
experiment 0.40 g of BPO was added to 50 mL of toluene, under mechanical stirring in a 100 mL
round bottom flask. 2-propanol (10 mL) was added to the above solution. 1.5 mL of DBSA, 0.2
mL of aniline and 10 mL (0.6M CuCl2) solution in deionized water was added to the above
mixture to form a white milky emulsion. 10 mL of 1% PVA solution was also added to the above
mixture. The reaction was allowed to proceed for 24h. After 24h the aqueous and organic layers
were separated in a separating funnel. The organic layer was extensively washed with acetone to
remove the unreacted material. The product obtained was transferred into a petri dish and dried
in oven for 24h at 40 0C. The polymer was broken in to flakes by the addition of small amount of
acetone. The polymer was separated from the petri dish and labeled as PANI-Cu-PVA. Several
different concentrations of CuCl2 and PVA solutions were investigated. The same procedure was
repeated to synthesize PANI, PANI-Cu, and PANI-PVA. The PANI samples were synthesized
38
without the addition of CuCl2 and PVA. The PANI-Cu was synthesized without the addition of
PVA solution and PANI-PVA was synthesized without the addition of CuCl2 solution.
2.9.3 Characterization
The synthesized material was characterized by using the following techniques.
2.9.3.1 Conductivity and Mass Measurement
The conductivity measurements of PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA
were carried out by using four point probes Jandel Model RM2. Four electrical contacts were
made with the solid pellet compressed under high pressure of 800 bar.
2.9.3.2 UV/Vis Spectroscopy
UV/Vis spectra were recorded by using Shimadzu UV/Vis 1700 Spectrophotometer. The
selected spectral region was from 900 to 200 nm, with a sampling interval of 0.5 nm.
2.9.3.3 FTIR spectroscopy
IR Prestige-21 FTIR Spectrophotometer Shimadzu Japan was used to record the FTIR
spectra. The numbers of scans for each sample was 10 and the spectral region rang was 400 to
4000 cm-1.
2.9.3.4 Thermogravimetric Analysis
The TGA was performed by using Diamond TG/DTA Perkin Elmer USA, on solidsamples at a temperature range from 30 to 600 0C at the Centralized Resource Laboratories,University of Peshawar, Pakistan.
2.9.3.5 X-ray Diffraction Measurement
Siemens diffractometer D 5000 at the Polymer Electronic Research Centre, University of
Auckland, New Zealand was used to carry out the XRD of solid samples.
2.9.3.6 Scanning Electron Microscopy
The SEM images were taken in Centralized Resource Laboratories, University of
Peshawar, Pakistan by using scannining electron microscope Model JSM-5910 JEOL Japan.
39
2.9.3.7 Cyclic Voltammetry
Cyclic voltammetry (CV) was carried out by using ALS/DY 2323 Biopotentiostate in
National Centre of Excellence in Physical Chemistry, University of Peshawar, Pakistan. Gold
foil was used as working electrode and gold coiled wire as counter electrode. The calomel
electrode was used as reference. A thin film of the polymer was deposited on the gold electrode
and the CVs were recorded in 0.5M H2SO4 solution as supporting electrolyte. The scan rate was
50 mV S-1.
***********************
40
3. RESULTS AND DISCUSSION
3.1 pH Measurement and Mass Yield Calculations
The measurement of pH and mass yield are important tools to observe the course of
aniline polymerization. Normally a decrease in pH is observed due to the release of protons
during aniline polymerization and the mass yield is associated with change in pH as discussed in
previous literature [91].
Table 3.1. Initial and Final Solution pH and Mass Yields for Reactions with Various Oxidant to
Monomer Ratios R
R Initial pH Final pH Mass yield (g)
1 4.70 4.22 0.017
2 4.85 3.72 0.028
3 4.82 3.60 0.034
4 4.72 3.17 0.026
5 4.78 2.67 0.037
6 4.70 2.69 0.034
7 4.78 2.62 0.038
8 4.82 2.36 0.050
9 4.78 2.29 0.050
10 4.81 2.18 0.052
11 4.80 2.27 0.054
12 4.75 2.13 0.054
41
13 4.72 2.08 0.057
14 4.75 1.87 0.067
15 4.73 1.70 0.076
Table3.1 shows the initial pH, final pH, and mass yields for aniline polymerizations with
various oxidant to monomer ratios R. From Table 3.1 it is clear that the final pH decreases and
the reaction yield increases with an increase in the oxidant to monomer ratio. This increase in the
yield is most likely due to an increase in the oxidation potential of CuCl2 with an increase in its
molar concentration [88]. The generally low yield of reaction is attributed to the co-formation of
a copper(II) chloride-aniline complex [87]. In the present study this complex was removed by
washing with water and acetone.
Table 3.2. Weight (%) Loss of B-PANI after washing with HCl, NH4OH and N2H4 and
corresponding Mass Yield of H-PANI, DB-PANI and PANIa
% Loss with HCl/
Mass yield H-PANI
% Loss with NH4OH/
Mass yield of DB-PANI
% Loss with N2H4/
Mass yield of PANI
81±5
0.0157a
67±5
0.0246
54±5
0.0352
aThe mass yields of DH-PANI, RB-PANI, R-PANI and RH-PANI (Scheme 1) were 0,0121, 0.0157,
0.0243 and 0.0093 g respectively.
Table 3.2 shows that the % weight lost during washing with HCl, NH3 and N2H4 solutions
is very high, which is an indication of the presence of a large amount of Cu2(OH)3Cl,[87] which
is responsible for the nonconductive behavior of the B-PANI products. The mass yields (Table 2)
are a small percentage (ca. 10% or less) of the mass of aniline used in the reaction (0.204 g),
indicating that the percentage yields based on aniline are quite low. The H-PANI product with R
= 15 shows a conductivity of 2.3×10-1S cm-1.
42
3.2 FTIR Spectroscopy
All the data in the subsequent discussion are for the R=15 case.
Figure 3.1. FTIR spectrum of the initial product (R = 15) before washing.
The FTIR spectrum of the initial product obtained from the reaction in which the oxidant
(CuCl2) to monomer (aniline) mole ratio R = 15 before washing is shown in Fig. 3.1.
Comparison of this spectrum with literature data showed close similarities between this product
and that obtained by Le Cocq et al. [87]. The presence of two narrow bands around 1601 and
1567cm-1 show that the product is a 1:2 complex of copper(II) chloride with aniline which is
similar to that reported earlier [87]. Another similarity with the said report is the presence of two
bands at 3443 and 3368 cm-1 indicating the presence of an inorganic basic copper(II) chloride
product similar to Cu2(OH)3Cl that was observed in a previously reported study [87]. Since the
reaction is carried out in water, a possible mechanism for the formation of Cu2(OH)3Cl is as
follows:
C6H5NH2 + H2O→ C6H5NH3+ + OH− (1)
2CuCl2 + 3OH−→Cu2(OH)3Cl + 3Cl− (2)
43
When the initial product was extensively washed with milli-Q water followed by washing with
acetone, the peaks of the CuCl2/aniline complex disappeared and those of the basic copper(II)
chloride were shifted to 3512 and 3430 cm-1, close to the positions for Cu2(OH)3Cl, [87] as
shown by the spectrum of the product B-PANI in Fig. 3.2A(a).
cm-1
1000200030004000
%T
30
40
50
60
70
80
90
100
110
a
b
c
3.2A
cm-1
1000200030004000
%T
50
60
70
80
90
100
110
a
b
3.2C
cm-1
1000200030004000%
T
20
40
60
80
100
120
a
b
3.2B
cm-1
1000200030004000
%T
70
80
90
100
110
120
a
b
3.2D
Figure 3.2. FTIR spectra of A(a) B-PANI, (b) H-PANI(c) PANI, B(a) DB-PANI and (b) RB-
PANI, C(a) PANI and (b) R-PANI, D(a) DH-PANI and (b) RH-PANI.
In Fig. 3.2A(a) B-PANI the peaks at 1580 and 1488 cm-1 are assigned to the quinoid and
benzenoid unit of polyaniline. The peaks at 1315 and 1243 are attributed to the C-N and C=N
44
stretching modes. The bands at 1142 and 819 cm-1are assigned to the C-H in-plane and out-of-
plane bending modes [17]. The two intense peaks at 3512 and 3430 cm-1 are assigned to the O-H
stretching modes of Cu2(OH)3Cl [87].
Washing the product B-PANI with 1M HCl produces H-PANI whose FTIR spectrum is
shown in Fig. 3.2A(b). From this it is evident that the peaks for Cu2(OH)3Cl have disappeared.
This is attributed to dissolution of the Cu2(OH)3Cl in the HCl to form soluble CuCl2. Treatment
of B-PANI with 35% hydrazine produces PANI, whose FTIR spectrum is shown in Fig. 3.2A(c).
This shows that the peaks for Cu2(OH)3Cl can also be removed by reduction with hydrazine.
This is attributed to reduction of the copper(II) compound Cu2(OH)3Cl to copper(I) chloride,
with consequent removal of the OH stretching bands from the spectrum. The remaining peaks in
H-PANI and PANI are in good agreement with those of the emeraldine base (EB) form of
polyaniline [90].
The FTIR spectra of the products obtained by dedoping of B-PANI with 10% aqueous
ammonia (DB-PANI) followed by reduction with 35% hydrazine (RB-PANI) are shown in Fig.
3.2B (a), (b) respectively. In the spectrum of DB-PANI (Fig. 3.2B (a)) the peaks at around 1583
and 1481 cm-1 are assigned to the quinoid and benzenoid group of PANI. In RB-PANI
(Fig.3.2B(b)) the intensity of the peak at 1583 cm-1 is reduced and that at 1481 cm-1 is increased
indicating the reduction of sample by hydrazine [90].
In Fig. 3.2C the spectrum of PANI (Fig. 3.2C(a)) is compared with that of the product R-
PANI, obtained when the sample B-PANI is treated with 35% hydrazine and then further
reduced with 50% hydrazine for 24h (Fig. 3.2C(b)). A clear decrease in the intensity of the peak
at around 1588 cm-1 for the quinoid unit of PANI is observed as compared to the benzenoid unit
of PANI at around 1492 cm-1. This is attributed to the reduction of the EB form to
leucoemeraldine base (LB). The presence of a weaker peak at 1588 cm-1 indicates that a small
amount of quinoid units are still present in the polymer chain [90].
The FTIR spectra of the products obtained by dedoping of H-PANI with 10% aqueous
ammonia (DH-PANI) followed by reduction with 50% hydrazine for 24 hours (RH-PANI) are
shown in Fig. 3.2D(a), (b) respectively. A significant decrease in the intensity of the peak at
around 1594 cm-1 for the quinoid unit of PANI is shown by the spectra RH-PANI confirming the
reduction of sample [90]. This is attributed to the conversion of quinoid units into the bezenoid
45
units by the addition of hydrogen from hydrazine and evolution of nitrogen gas from the reaction
mixture.
3.3 UV/Vis Spectroscopy
Generally there is a strong absorption in the regions of 320-330 nm and 600-660 nm in
the UV/Vis spectra of the emeraldine base (EB) form of PANI. The band at 320-330 nm is
assigned to a π−π* transition of the bezenoid unit while the band at 600-660 nm is attributed to
the excitation of the quinoid segment [92].
The UV/Vis spectra of B-PANI, H-PANI and PANI are shown in Fig. 3.3A (a), (b) and
(c) respectively. The peaks at around 320-330 show the π−π* transition in the benzenoid segment
[93], while the peak for the quinoid segment of polyaniline in B-PANI and H-PANI is shifted
towards lower wavelength. FTIR (Fig. 3.2 A(a), B-PANI) and XPS (Fig.3.4 (a), H-PANI) data
indicate that copper(II) is still present in these products, and this wave number shift is possibly
due to a contribution from copper(II) chromophores.
46
a
b
c
nm
300 400 500 600 700 800 900
Abso
rban
ce
0.0
0.5
1.0
1.5
2.0
2.5
B-PANIH-PANIPANI
a
b
c
33.3A
nm
300 400 500 600 700 800 900
Abs
orba
nce
0.0
0.2
0.4
0.6
0.8
1.0
PANIR-PANI
a
b
3.3C
300 400 500 600 700 800 900
Abso
rban
ce
0.0
0.5
1.0
1.5
2.0
RB-PANIDB-PANI
nm
a
b
3.3B
nm
300 400 500 600 700 800 900
Abs
orba
nce
0.0
0.5
1.0
1.5
2.0
DH-PANIRH-PANI
H-PANIa
b
c
3.3D
Figure 3.3. UV/Vis spectra of A(a) B-PANI, (b) H-PANI, (c) PANI, B(a) DB-PANI (b) RB-
PANI, C(a) PANI, (b) R-PANI, D(a) H-PANI, (b) DH-PANI and (c) RH-PANI.
The UV/Vis spectra of DB-PANI and RB-PANI are shown in Fig.3.3B (a) and (b). In
Fig. 3.3B(a) the UV/Vis spectrum of DB-PANI is the same as that of B-PANI in Fig. 3.3A(a),
suggesting that dedoping was ineffective, which is consistent with the forthcoming XPS results,
while the spectrum of RB-PANI (Fig. 3.3B(b)) indicates the reduced form (LB)-PANI. In the
spectrum of DB-PANI (Fig. 3.3B (a)) the peak for the quinoid unit has a similar shift towards
lower wavelength as discussed earlier for Fig.3.3A (a) and (b). The UV/Vis spectrum of RB-
PANI (Fig. 3.3B(b)) shows an increase in the intensity of peak for benzenoid unit, and decrease
47
in the intensity of peak for quinoid unit, which is consistent with reduction to the LB-PANI form
[94].
Fig. 3.3C shows the UV absorption spectra of PANI and its reduced form R-PANI. In the
R-PANI (Fig. 3.3C (b)) the absorption peak for the quinoid unit at around 600-650 nm tends to
disappear relative to that of PANI (Fig. 3.3C (a)), which indicates the reduction of the sample to
the LB-PANI form [94]. Both PANI and R-PANI were obtained from their precursors by
treatment with 35% N2H4 (Scheme 1); the fact that R-PANI was not produced directly from the
B-PANI is attributed to the fact that all the N2H4 was used up in converting the basic copper(II)
chloride present in this sample to copper(I) chloride.
Fig. 3.3D shows the UV absorbance spectra of H-PANI, DH-PANI and RH-PANI.DH-
PANI (Fig. 3.3D (b)) and RH-PANI (Fig. 3.3D (c)) exhibit absorption at 320-330 nm and at
around 620-660 nm, which is similar to the emeraldine (EB) form of polyaniline [92]. In the RH-
PANI (Fig. 3.3D (c)) the peak at around 620-660 nm tends to disappear indicating the reduction
of EB to the LB form [94]. The conclusions from the UV absorption spectra of H-PANI, DH-
PANI and RH-PANI are in good agreement with those from the FTIR spectra.
3.4 Elemental Analysis
The elemental analysis results for the DB-PANI and H-PANI products are shown in
Table. 3.3. The C/N ratios are close to, but slightly higher than, the theoretical value of 6.0 for
PANI. The results given in the Table 3.3 for DB-PANI and H-PANI are given in the same form
as those for the EB form of PANI reported in Zeng et al. [90], i.e. it gives the ratio C:H:N
calculated from the elemental analysis data; however, there must be a significant amount of other
elements present as the sum of the C, H, N content is only 67%. The % of C,H,N values for
undoped EB-PANI add to 100% (Table 3.3), and are all considerably higher than the
experimental values for H-PANI and DB-PANI. If the PANI were present as ES-PANI with Cl-
as the dopant (i.e. the EB-PANI 2HCl salt), lower values would be obtained (Table 3.3), but
these are still significantly higher than the experimental values. Under the experimental
conditions used to produce these materials (excess CuCl2 in solution) it is possible that the
chloride dopant ions could associate with a CuCl2 molecule to produce a [CuCl4]2- dopant to
produce EB-PANI H2CuCl4 salt as the product, for which the calculated %C,H,N (Table 3.3) are
48
in much closer agreement with the observed values. In order to investigate this further, the H-
PANI and DB-PANI products were examined by XPS.
Table 3.3. Compositions of DB-PANI and H-PANI for oxidant to monomer ratio R = 15
Sample %C %H %N Composition C/N ratio
DB-PANI
H-PANI
EB-PANI
ES-PANI
(2HCl salt)
ES-PANI
(H2CuCl4 salt)
ES-PANI (30%
ox; 2HCuCl3 salt)
ES-PANI (30%
ox; 1.8HCuCl3
salt)
53.68
52.84
79.54
66.21
50.59
50.72
52.62
3.79
4.30
5.01
4.63
3.54
3.55
3.66
9.92
10.06
15.46
12.87
9.84
9.86
10.23
C24H20.23N3.80 +?
C24H23.44N3.91 +?
C24H18N4
C24H20Cl2N4
C24H20CuCl4N4
C24H20Cu1.2Cl3.6N4
C24H19.9Cu1.1Cl3.2N4
6.3
6.1
6.0
6.0
6.0
6.0
6.0
49
3.5 X-Ray Photoelectron Spectroscopy
Cu 2p XPS for H-PANI and DB-PANI are shown in Fig. 3.4. The spectrum of H-PANI
shows a strong Cu 2p signal which is completely absent in the DB-PANI product. The binding
energies of the Cu 2p3/2 and Cu 2p1/2 peaks at 933.4 eV and 953.3 eV (2:1 area ratio) are
characteristic for Cu(II), as are the characteristic shake up satellites ~7 eV above the main Cu 2p
lines. The satellite peak areas are ~36% of the total Cu 2p signal area. This is typical for copper
(II) containing compounds such as CuO. NH4OH treatment of the B-PANI product removed all
of the copper(II), whereas HCl treatment of the same material did not. This is consistent with
proposal above that the PANI formed in the CuCl2 oxidative polymerization is in the form of the
EB-PANI H2CuCl4 salt. The copper(II) that is contained in B-PANI would not be removed by
treatment with HCl, and it would still be present in the H-PANI product, but it would be
removed (as [Cu(NH3)4]2+ 2Cl-) by treatment with NH4OH, and would therefore be absent in the
DB-PANI product, as observed experimentally. Also consistent with this, is the fact that the XPS
data also showed the presence of Cl, and that the Cl content is reduced in the DB-PANI product.
However, the Cl/Cu ratio in H-PANI estimated from the XPS signal intensities (2.6) is closer to
3 as compared to the value 4 expected if the dopant were [CuCl4]2-. This suggests that the dopant
is [CuCl3]- (or an oligomeric or polymeric form thereof), and that the material is therefore the
EB-PANI 2HCuCl3 salt. [CuCl3]- would be a more likely dopant than [CuCl4]
2- under the
conditions of the synthesis (excess CuCl2 present) However, this does not provide a good
agreement with the composition determined by elemental analysis as the %C, H, N values for
this form is too low. The surface sensitivity of the XPS technique may be responsible for the
discrepancy in the Cl/Cu ratio. The XPS signal comes from the top 1-2 nm of the PANI samples.
Surface leaching of chloride during post synthesis washings could have partially removed
chloride from the near surface region of the samples (while leaving the bulk composition
determined by elemental analysis largely unaffected).
50
Figure 3.4. Cu 2p XPS for (a) H-PANI, and (b) DB-PANI.
A further variable relevant to the composition of PANI materials is the degree of
oxidation (or oxidative doping level) and this can be determined by XPS by examining the
oxidation states of N present, via the N 1s [95] signal. N 1s XPS for H-PANI and DB-PANI are
shown in Fig. 3.5. The N 1s data for both samples can be fitted using a combination of sub-
spectra due to oxidized (-NH2+-, =NH+-) and neutral (-NH-, =N-) nitrogen environments. Results
of the curve-fitting are shown in Table 3.4 which indicates a degree of oxidation of ca. 0.3 for
both products. The fact that the same value is obtained for both is consistent with the expectation
that acid/base doping/dedoping should not change the degree of oxidation. The degree of
oxidation is less than the value 0.5 corresponding to the ES-PANI form, and this is consistent
51
with the expectation that a weaker oxidant such as CuCl2 might not achieve as high a degree of
oxidation as a stronger oxidant such as APS. The degree of oxidation also determines the
maximum level of acid doping. Combination of the results of the XPS analyses for the H-PANI
product (30% oxidation, [CuCl3]- dopant) results in the composition [(C12H10N2)1-
x(C12H10N22+)x[CuCl3
-]2x with x = 0.3. This yields % C, H, N values that are in reasonable
agreement with the observed values (Table 3). Further improvement in the agreement is obtained
if the possibility of partial doping of the polymer is considered. It is well known that EB PANI
can only be fully acid doped (2H+ per two oxidized N atoms) in solutions of low pH, near pH = 0
[24] In the CuCl2 oxidation experiments, the pH only fell to 1.7 in the R = 15 case. Therefore,
the degree of doping would be expected to be less than 2HCuCl3 per two oxidized N atoms. In
the last row of Table 3.3 the results for 1.8CuCl3 per two oxidized N atoms have been added,
resulting in much better agreement with the observed %C, H, N values.
52
Figure 3.5. N 1s XPS for (a) H-PANI, and (b) DB-PANI.
53
Table 3.4. Speciation of Nitrogen in PANI samples from N 1s Peak Analysis
Sample Percentage of total N Nox/Ntotal
2HN
402.5 eV
HN
401.1 eV
NH
399.7 eV
N
398.4 eV
H-PANI 4.7 23.5 52.8 19.0 0.28
DB-PANI 7.4 22.9 63.2 6.5 0.32
3.6 Soft X-ray Spectroscopy
Fig. 3.6 shows the nitrogen K edge NEXAFS spectra of (a) B-PANI, (b) DB-PANI, and
(c) RB-PANI. The spectra contain an intense feature at around 397.4 eV, in B-PANI, DB-PANI
and RB-PANI which is likely to arise from the =N- quinoid ring of the emeraldine base form
[96]. The intensity of this peak for the quinoid unit of polyaniline in the RB-PANI is less
compared to those of B-PANI and DB-PANI, which confirms that the sample has been reduced.
This is supported by the fact that the peak at 402.3 eV gains intensity as the peak at 397.4 eV
peak was attenuated. The 400.1 eV peak is assigned to the three electron =N--bonding in the
emeraldine base form of PANI [96]. The 402.3 eV peak is due to -NH- in PANI emeraldine base
forms[96]. The broad peak above 406 eV is due to delocalized sigma* resonances [97]. The
observations in Fig. 3.6 are consistent with those seen in the FTIR and UV/Vis for these
materials.
54
Figure 3.6. NEXAFS of (a) B-PANI (b) DB-PANI (c) RB-PANI.
3.7 Solid state NMR
Fig. 3.7 shows the solid state 13C NMR of the sample DH-PANI. The solid state NMR
spectra show peaks at 118.580, 130.163, 133.472, 142.296 and 155.533 ppm. Based on previous
related work [98-101] the assignment of these peaks is shown in Table 3.5 which are similar to
the EB form of PANI reported in literature. The peak at 118.580 and 130.163 ppm are assigned
to C-6 and C-2,3 respectively. The peaks for the C-7,8 of the quinoid unit of EB PANI appear at
155.533 and 133.472 respectively. The peak at 142.296 is assigned to C-4,5.
55
Figure 3.7. 13C Solid State NMR spectra of DH-PANI.
Table 3.5.Peak assignment in the SSNMR of EB form of PANI
* NH NH Nn
N
2 3
3
1
2
4 5
6
6
5 4
3
36
6
2
2
1 7
8
8
8
8
7
13C chemical shift Assignment (carbon number)
118.580 C-6
130.163 C-2, 3
133.472 C-8 Quinoid unit
142.296 C-4, 5
155.533 C-7 Quinoid unit
56
3.8 SEM Analysis
The SEM images of B-PANI, H-PANI and DB-PANI are shown in Fig. 3.8 (a), (b) and
(c) respectively. The images show the spherical morphology of particles as reported in previous
literature [17]. In the work reported by Ding et al. [102], they have prepared PANI nanofibers
whereas we have obtained the PANI nano particles. The average particle size of B-PANI and H-
PANI is 660 nm, 350 nm respectively. The material is highly porous and has irregular pore size
[103].
Figure 3.8. SEM analysis of (a) B-PANI, (b) H-PANI, and (c) DB-PANI.
56
3.8 SEM Analysis
The SEM images of B-PANI, H-PANI and DB-PANI are shown in Fig. 3.8 (a), (b) and
(c) respectively. The images show the spherical morphology of particles as reported in previous
literature [17]. In the work reported by Ding et al. [102], they have prepared PANI nanofibers
whereas we have obtained the PANI nano particles. The average particle size of B-PANI and H-
PANI is 660 nm, 350 nm respectively. The material is highly porous and has irregular pore size
[103].
Figure 3.8. SEM analysis of (a) B-PANI, (b) H-PANI, and (c) DB-PANI.
56
3.8 SEM Analysis
The SEM images of B-PANI, H-PANI and DB-PANI are shown in Fig. 3.8 (a), (b) and
(c) respectively. The images show the spherical morphology of particles as reported in previous
literature [17]. In the work reported by Ding et al. [102], they have prepared PANI nanofibers
whereas we have obtained the PANI nano particles. The average particle size of B-PANI and H-
PANI is 660 nm, 350 nm respectively. The material is highly porous and has irregular pore size
[103].
Figure 3.8. SEM analysis of (a) B-PANI, (b) H-PANI, and (c) DB-PANI.
57
3.9 Mechanism of PANI formation
A proposed mechanism of PANI formation by oxidation of aniline with copper chloride
is as follows: (see Figure 3.9)
4C6H5NH2 + 10 CuCl2 {[-C6H4-NH-]4}2+ + 8H+ + 10 CuCl2
-
where {[-C6H4-NH-]4}2+ is the emeraldine salt form of PANI the structure of which is given
below
Figure 3.9. Mechanism of PANI formation.
This differs from the mechanism reported in literature for the corresponding reaction
involving gold(III) chloride, in which the gold(III) is reduced to gold metal [17]. While the
formation of copper metal in the reaction of aniline with copper(II) has been proposed previously
[84], this seems unlikely in the present case because a rather strong reducing agent is required to
reduce copper(II) to copper(0), and in protic solvents copper(II) and copper(0) comproportionate
to copper(I). In the present study, the XPS showed that the copper in the product was present as
copper(II). If the above reaction were stochiometric, the dopant would be CuCl2- (copper(I))
rather than CuCl3- (copper(II)). However, because CuCl2 is in large excess in the reaction
mixture, copper(II) is more likely to be incorporated in the dopant anion than copper(I).
58
3.10 Results and Discussion (Part II)
3.11 pH measurement along with mass yield
Table 3.6 shows the mass of product relative to the mass of aniline monomer and the
oxidant to monomer ratio of the reactions. A decrease in final pH and the corresponding increase
in the yield of reactions were observed as the concentration of CuCl2 increases in the reaction
mixture. This increase in the yield is most likely due to an increase in the oxidation potential of
CuCl2 with an increase in its molar concentration [88].
Table 3.6. Oxidant to Monomer Ratio and Mass Yield along with initial and final pH
Oxi/Mon Initial pH Final pH Mass yield in grams
0.05 4.72 4.58 0.0171
0.25 4.85 4.60 0.0280
0.50 4.83 4.47 0.0342
0.75 4.70 4.37 0.0263
1.0 4.75 4.23 0.0373
1.25 4.71 4.10 0.0342
3.12 FTIR Spectroscopy
The FTIR spectra for pure emeraldine base (EB) and L-PANI samples are shown in
Fig.3.10 (a) and (b) respectively. The spectrum of pure EB shows intense peaks at 1585 and
1493 cm-1 which are assigned to the quinoid and benzenoid unit of polyaniline respectively. In
case of L-PANI sample the peak for the quinoid unit of polyaniline is absent while that of
benzenoid unit is shifted to1469 cm-1. The C-N stretching mode in L-PANI (Fig.3.10 b) is shown
by peak at 1209 cm-1 [33], while the C-H out of plane bending is shown by peak at 866 cm-1 [18].
In L-PANI (Fig. 3.10 b) another intense peak at 1290 cm-1 indicates the presence of secondary
amine [32]. From the FTIR spectra it is evident that the product L-PANI is the fully reduced
leucoemeraldine form of PANI.
59
Figure 3.10. FTIR spectra of (a) pure EB (b) L-PANI.
3.13 UV/Vis Spectroscopy
The UV/Vis spectra of polyaniline EB form shows strong absorption in the region from
320-340 nm and 600-660 nm which is due to the presence of benzenoid and quinoid units of
polyaniline [92]. The UV/ Vis spectra of pure EB and L-PANI sample are shown in Fig.3.11 (a)
and (b) respectively. The UV/Vis spectra of pure EB has two peaks at 629 and 324 nm while in
case of L-PANI sample the peak for the quinoid unit is absent indicating that the L-PANI sample
is the fully reduced leucoemeraldine form of PANI. The information provided by the UV/Vis is
in agreement with the FTIR spectra in Figure 3.10.
60
Figure 3.11. UV/Vis spectra of (a) pure EB (b) L-PANI.
3.14 Elemental Analysis
Table.3.7 shows the results of elemental analysis of L-PANI sample. The percentage of C,
H and N were found to be 76.87, 5.64 and 15.20 respectively, which are close to the theoretically
calculated values for leucoemeraldine form of polyaniline. The percentage of hydrogen is found to
be more than expected which may be due to the presence of water molecule [90]. The C/N ratios
from elemental analysis are close to the expected value of 6.0.
Table 3.7. Elemental Analysis Results of L-PANI
Sample Oxi/Mon %Yield % C % H % N Composition C/N ratio
L-PANI 1 23 76.87 5.64 15.20 C24H20.06N4.07.(H2O)0.5 5.89
61
3.15 Results and discussion (Part III)
3.16 Mass yield and conductivity measurements
Table 3.8 shows the calculated mass yield for various PANI-Cu products and their
conductivities measured by four point probe instrument. Table1 shows that the mass yield of the
composite PANI-Cu decreases as the molar concentration of CuCl2 solution increases in the
reaction mixture. This decrease in mass yield may be attributed to the formation of copper
aniline complex [87] in addition to the formation of PANI-Cu products. The conductivity data
shows the decrease in conductivity of the composite which could be attributed to the partial
blocking of conductive path by Cu particle in the PANI matrix [104, 105], however, these values
are in good agreement with the data reported in [106].
Table 3.8. Mass Yield and Conductivity of PANI and its Composites with Cu
Sample Mass yield (g) Conductivity (S/cm)
PANI 0.192 1.92×10-2
PANI-Cu 0.2 0.0974 5.13×10-3
PANI-Cu 0.4 0.0664 2.14×10-4
PANI-Cu 0.5 0.0491 4.34×10-4
PANI-Cu 0.6 0.0133 4.81×10-4
PANI-Cu 0.7 0.0123 4.83×10-4
3.17 UV/Visible Spectroscopy
The UV/Vis spectra of polyaniline show strong absorption in the region from 320-330
nm and 600-660 nm. These peaks are assigned to the π−π* and n−π* transition of the benzenoid
and quinoid units of polyaniline respectively [92].
The UV/Vis spectra of PANI, PANI-Cu 0.2, PANI-Cu 0.4, PANI-Cu 0.6 and PANI-Cu
0.7 are shown in Figure 3.12 (a), (b), (c), (d), and (e) respectively. The peaks at 326-328 nm
62
indicate the π−π* transition of benzenoid units of polyaniline [93]. In case of PANI-Cu 0.2,
PANI-Cu 0.4, PANI-Cu 0.6 and PANI-Cu 0.7 the peak for the quinoid units of polyaniline has a
blue shift. This blue shift may be attributed to the presence of Cu II chromophores. The spectra
also indicate that the blue shift becomes more prominent with the increase in CuCl2
concentration. Such kind of blue shift has been reported for the presence of TiO2 in polyaniline
by Karim et al. [107].
Figure 3.12. UV/Vis spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4, (d) PANI-Cu 0.6and (e) PANI-Cu 0.7.
3.18 FTIR Spectroscopy
Figure 3.13 shows the FTIR spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4, and
(d) PANI-Cu 0.6. In Fig. 3.13 (a), (b), (c), and (d) the peaks at around 1492 and 1581 cm-1 are
attributed to the benzenoid and quinoid unit of polyaniline. The bands at 1232 and 1301 cm-1 are
attributed to the C=N and C-N stretching modes. The peaks at 829 and 1139 cm-1are assigned to
the C-H out-of-plane and in-plane bending mode [17]. In Fig. 3.13 (b), (c) and (d) the peak for
quinoid unit at 1581 gains intensity as the concentration of CuCl2 increases in the reaction
mixture indicating the interaction of CuCl2 with the nitrogen atom of quinoid unit of polyaniline
[108], however, in our case the peak for quinoid unit of PANI has not been blue shifted, which
63
may be due to the low concentration of CuCl2 solutions and co-formation of Cu-aniline complex,
as discussed earlier. The FTIR spectra are mostly dominated by the polyaniline signals and thus
the polymer-metal interaction is not very clear [20].
Figure 3.13. FTIR spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4, and (d) PANI-Cu0.6.
3.19 Thermogravimetric Analysis (TGA)
The thermal stability of synthesized PANI and PANI-Cu was tested by using TGA. The
samples were kept for one minute at 30 oC and then heated from 30 °C to 600 oC at a rate of 10oC/minute. The loss in mass for PANI and PANI-Cu composite upon heating under nitrogen
atmosphere is shown in Fig. 3.14 (a) and (b) respectively. A steady mass decrease is found up to
296oC both in case of PANI Fig.3.14 (a) and PANI-Cu Fig.3.14 (b). A rapid change in mass
occur in the range from 300-400oC in both the samples but in case of PANI the % weight loss is
more as compared to PANI-Cu which indicates greater stability of PANI-Cu as compared to
PANI. The weight lost at low temperature is attributed to the expulsion of water from the
polymer structure while at high temperature the degradation of polymer chain takes place due to
the removal of acid dopant. After the removal of acid dopant the decomposition of polymer
skeleton occurs at even higher temperature [109]. The weight loss of PANI and PANI-Cu
64
composite at 600oC was 68.06% and 42.01% respectively. The data indicate the improvement in
the thermal stability due to the inculcation of metal particles in the PANI matrix [107].
Figure 3.14. TGA analysis of (a) PANI and (b) PANI-Cu.
3.20 X-ray Diffraction (XRD)
The XRD is a nondestructive and helpful technique used to identify the crystallinity of
solid materials. Fig. 3.15 (a) and (b) show the XRD of PANI and PANI-Cu respectively. For
PANI and PANI-Cu the characteristic peak appears at 2θ = 25o, 19o and 13o indicating that both
the samples were amorphous [16]. Since the XRD peaks for PANI-Cu are mostly similar to that
of the free PANI so this suggests that the structure of CuCl2 may be distorted during the process
of polymerization [110], moreover, the peaks for PANI sample are slightly sharper than PANI-
Cu which suggests that the PANI sample is more crystalline than PANI-Cu. This is in agreement
with the conductivity data as discussed in Section 3.16 (Table 3.8).
65
Figure 3.15. XRD analysis of (a) PANI and (b) PANI-Cu.
3.21 Scanning Electron Microscopy (SEM)
The SEM images of PANI and PANI-Cu are shown in Fig. 3.16 (a) and (b) respectively.
The PANI sample i.e Fig. 3.16 (a) has an uneven irregular surface morphology as reported in
previous literature [57]. In case of PANI-Cu, Fig. 3.16 (b) the irregularity of surface has
increased and appears to be more porous than PANI [111]. The pore size in PANI-Cu is uneven
and larger as compared to PANI. Although the surface morphology of the composite PANI-Cu
does not differ much from the pure PANI, when CuCl2 is added, the pore size of composite
become larger, which leads to the change in morphological structure from firm gravel to lose
cotton appearance.
66
Figure 3.16. SEM images of (a) PANI and (b) PANI-Cu.
3.22 Cyclic voltammetry (CV)
Cyclic voltammetry (CV) was carried out to study the redox properties of synthesized
material by using gold as working electrode. The calomel electrode was used as reference. On
the gold foil electrode a thin film of the polymer was deposited and the CVs were recorded with
a scan rate of 50 mV S-1 in 0.5M H2SO4 solution as supporting electrolyte.
The cyclic voltamograms of the synthesized PANI and PANI/PVA composite are shown
in Fig. 3.17 (a) and (b) respectively. The PANI sample, Fig. 3.17 (a), shows two redox peaks (I
and II). The conversion of fully reduced neutral leucoemeraldine (LE) form of PANI to partially
oxidized emeraldine base (EB) form of PANI is shown by the peak at ESCE= 0.109V, while the
conversion of partially oxidized EB form to the fully oxidized pernigraniline state of PANI is
shown by the peak at ESCE= 0.650V [112, 113]. In the reverse scan the conversion of
pernigraniline to emeraldine and then from emeraldine to leucoemeraldine state is shown by the
peak I/ and II/ at ESCE= -0.046V and ESCE= 0.6130V respectively [57]. The peak I and II in case
of PANI-Cu appears at ESCE= 0.104V, and ESCE= 0.63V respectively which are slightly shifted
toward the left indicating the presence of metal in the sample [114]. In the reverse scan the peaks
I/ and II/ appear at ESCE= 0.0180V and ESCE=0.594V respectively for PANI-Cu composite. The
cyclic voltamogram of PANI-Cu shows that the composite is electro active and show two
oxidation/reduction peaks just like PANI [114].
67
Figure 3.17 CVS of (a) PANI and (b) PANI-Cu.
3.23 In situ UV/Vis Spectroscopy
The UV/Vis spectra of PANI and PANI-Cu film, deposited on ITO coated glass electrode
at various electrode potentials ERHE = 0.0 to 0.8 is shown in Fig. 3.18 (a) and (b) respectively.
Three characteristic absorption bands can be seen. The band at around λ= 315 nm is attributed to
the π−π* transition of the benzenoid units of reduced PANI [115, 116]. This peak is shifted to
360 nm in the spectra of PANI-Cu product. The band at λ= 420 nm showing maximum intensity
at ERHE = +0.3 is attributed to an intermediate redox state of the PANI film, which possibly
possesses non conjugated benzenoid units in a polymer chain [115-119]. In the red region of the
UV/Vis spectra the main absorbance band is assigned to the emeraldine form of PANI. This peak
is also shifted towards the lower wavelength with increase in potential as reported earlier [119].
A decrease in the intensity of the band at λ= 315 nm and a progressive increase in the intensity of
the band in the red region is observed by shifting the electrode potential to higher values,
indicating a decreasing number of benzenoid rings and increasing number of quinoid rings
because of oxidation of the leucoemeraldine into the emeraldine form of PANI. This behavior is
more prominent in PANI as compared to PANI-Cu product.
68
Figure 3.18. UV-Vis spectra of (a) PANI and (b) PANI-Cu film, deposited on ITO coated glass
electrode, obtained at different electrode potential values ranging from ESCE= 0.0 TO 0.8 V at an
interval of 0.1 V.
Fig. 3.19 (a) and (b) show the dependence of absorbance on potential at three different
wavelengths [(315 and 360 nm), 420 nm, and 750 nm] derived from Fig.3.18 (a) and (b). A
decrease in absorbance at λ= 315 and 360 nm is observed by sweeping the potential to higher
values which is attributed to the conversion of benzenoid segments to quinoid segments of
69
PANI [115]. The absorbance maxima for the band at λ= 420 nm is observed at around ERHE =
+0.3 V which is assigned to the intermediates formed during the electro oxidation of
leucoemeraldine form of PANI [117-119]. A progressive increase in the absorbance band at λ=
750 nm with the increase in potential indicates the increase in quinoid units of emeraldine form
of PANI [119].
Figure 3.19. (a) and (b) Absorbance vs. Potential at three selected wavelengths, derived
from the above displayed spectra in Fig. 3.18 (a) and (b).
70
3.24 Results and Discussion (Part IV)
3.25 Conductivity Measurements and Mass Yield
The mass yield calculated for various PANI/PVA products and their conductivity
measurement by four probe instrument are shown in Table 3.9. The results in Table 3.9 show
that the mass yield of the PANI/PVA decreases as the percentage of PVA solution increases in
the reaction mixture. This decrease in mass yield may be attributed to hydrogen bonding between
hydrogen of hydroxyl group of PVA and nitrogen of aniline due to which the aniline
polymerization is inhibited [120]. The conductivity data obtained from the four point probe
instrument show that the composite containing 3% PVA has maximum conductivity i.e.
6.66×10-2 S/cm. This is further supported by the XRD data (see below, Fig. 3.23 (b) PANI/PVA)
that the conductivity increases with the increase in crystallinity [121]. Beyond 3% PVA content,
the conductivity of the composite decreases which can be attributed to the increase of non
conducting PVA content with respect to conducting PANI contents in the composite [122, 123].
Table 3.9. Mass Yield and Conductivity of PANI and its Composites with PVA
Sample Mass yield (g) Conductivity (S/cm)
PANI 0.1927 1.9×10-2
PANI/PVA 1% 0.1259 2.46×10-2
PANI/PVA 2% 0.1640 4.99×10-2
PANI/PVA 3% 0.1373 6.66×10-2
PANI/PVA 4% 0.1368 5.35×10-2
PANI/PVA 5% 0.1010 5.27×10-2
PANI/PVA 6% 0.1130 5.27×10-2
71
3.26 UV/Visible spectroscopy
The UV/Vis spectra of PANI and PANI/PVA are shown in Figure 3.20. The peaks at 326
and 633 nm [Fig.3.20 (a)] indicate the π−π* transition of benzenoid and quinoid segments of
polyaniline [93]. In PANI/PVA [Fig.20 (b)] these peaks for π−π*are red shifted to 335 and 645
nm respectively. This red shift may be attributed to the doping of PVA in PANI matrix [124].
Figure 3.20. UV/Vis spectra of (a) PANI and (b) PANI/PVA.
3.27 FTIR Spectroscopy
Figure 3.21 (a) and (b) show the FTIR spectra of PANI and PANI/PVA respectively. The
characteristic bands in the spectrum of PANI [Fig. 3.21 (a)] are observed at 1581, 1508, 1311,
1138, 1028 and 827 cm-1. The frequency bands at 1581 and 1508 cm-1 are due to the presence of
quinoid and benzenoid ring of polyaniline respectively [17, 125]. The peak at 1311 cm-1 is
attributed to the C-N stretching mode of secondary aromatic amine [126]. The band at 1138 cm-1
has been assigned to the vibration of Q=+NH-B representing that the product PANI is in the
conductive emeraldine salt form of polyaniline [127]. The band at 1028 cm-1 is assigned to the
absorption of –SO3H group indicating that the PANI sample is also doped with DBSA. The peak
at 827 cm-1 is assigned to the C-H out-of-plane bending vibration [125]. The spectrum of
PANI/PVA shows all the characteristic peaks corresponding to the PANI spectrum and did not
72
show any additional peak thereby giving indication of no chemical interaction between PANI
and PVA [123]. However, in PANI/PVA spectrum the peak for the quinoid segment of
polyaniline is shifted from 1581 cm-1 to 1595 cm-1 which indicates the presence of hydrogen
bonding between PANI and PVA [120]. The FTIR spectra of PANI and PANI/PVA are
consistent with the UV/Vis spectra of PANI and PANI/PVA in Fig.3.20.
Figure 3.21. FTIR spectra of (a) PANI and (b) PANI/PVA.
3.28 Thermogravimetric Analysis (TGA)
Thermo gravimetric analysis (TGA) was performed to study the thermal stability of
synthesized PANI and PANI/PVA composite. The samples were heated from 30oC to 600 oC at a
rate of 10oC/minute after holding them for one minute at 30 oC. Fig.3.22 shows the loss in mass
for PANI and PANI/PVA composite upon heating under nitrogen atmosphere. A steady mass
decrease is observed up to 297 oC in both PANI (Fig.3.22 (a)) and PANI/PVA (Fig.3.22 (b)).
From 300-400oC a rapid change in mass is observed in both the samples but in case of
PANI/PVA the % weight loss from 350-400 oC is more as compared to PANI which indicates
that the stability of PANI is higher than that of PANI/PVA in the said temperature range. Beyond
400 oC the stability of PANI/PVA composite is greater as compared to PANI as the overall mass
loss in PANI/PVA is less than PANI. At low temperature the weight lost is attributed to the
removal of water from the polymer structure while the degradation of polymer chain takes place
73
at higher temperature due to the removal of acid dopant. At even higher temperatures, the
decomposition of polymer skeletal occurs after the removal of acid dopant [109]. The TGA
indicates the improvement in the thermal stability due to the incorporation of PVA in PANI
[124].
Figure 3.22. TGA curve of (a) PANI and (b) PANI/PVA.
3.29 X-ray Diffraction (XRD)
Most of the polymers are amorphous due to large volume fraction of amorphous phases.
Generally both PANI and PVA are amorphous. Fig.3.23 (a) and (b) show the XRD pattern of
PANI and PANI/PVA respectively. The PANI/PVA show the characteristic peak of PVA at
2θ=20o which confirms the presence of PVA in PANI [124]. The PANI and PANI/PVA samples
have peaks at 2θ=12o, 20o and 25o showing the amorphous nature [16]. However, the peak at
2θ=25o is more intense in PANI/PVA thus the crystallinity of PANI/PVA is increased by the
insertion of PVA [10]. This is further supported by the fact that the conductivity of PANI-PVA
has increased (see , Table 3.9) with the increase in crystallinity.
74
Figure 3.23. XRD of (a) PANI and (b) PANI/PVA.
3.30 Scanning Electron Microscopy (SEM)
Fig. 3.24 (a) and (b) show the SEM images of PANI and PANI/PVA respectively. The
SEM image of PANI [Fig.3.24 (a)] shows an irregular morphology. The irregular morphology of
PANI is also reported elsewhere [57]. From the SEM images it is quite clear that small granules
of PVA are present in the PANI matrix and the morphology of PANI is different from that of
PANI/PVA. The SEM image of PANI/PVA composite shows irregular shaped particles with
variable size. The irregular shape of PANI/PVA composite is attributed to the non compatibility
of two components [128]. Moreover, the PANI/PVA is more porous as compared to PANI [103,
129]. The surface of PANI is smoother than PANI/PVA and the sharp edges of PANI/PVA
particles can easily be correlated with the XRD data as discussed above (Fig. 3.23 (a), (b)). The
average particle size of PANI/PVA is 4 μm.
75
Figure 3.24. SEM images of (a) PANI and (b) PANI/PVA.
3.31 Cyclic Voltammetry (CV)
In order to investigate the redox properties of synthesized material cyclic voltammetry
(CV) was carried out by using gold as working electrode. Fig. 3.25 (a) and (b) show the cyclic
voltamograms of the synthesized PANI and PANI/PVA composite. The PANI sample show two
redox peaks (I and II). The peak at ESCE= 0.109V corresponds to the conversion of fully reduced
neutral leucoemeraldine form of PANI to partially oxidized emeraldine base (EB) form of PANI
while the peak at ESCE= 0.650V is due to the conversion of partially oxidized EB form to the
fully oxidized pernigraniline state of PANI [112, 113]. In the reverse scan peak I/ at ESCE= -
0.046V and II/ at ESCE= 0.6130V are attributed to conversion of pernigraniline to emeraldine and
then from emeraldine to leucoemeraldine state [57]. In case of PANI/PVA the peak I appears at
ESCE= 0.0830V, while the peak II retains its position at 0.65V. In the reverse scan the peak I/ and
II/ appears at ESCE= 0.0180V and 0.6380V for PANI/PVA composite. From the cyclic
voltamograms we can conclude that the PANI/PVA composite is electro active and show two
oxidation/reduction peaks just like PANI [130].
76
Figure 3.25. CVs of (a) PANI and (b) PANI/PVA on gold foil electrode (vs SCE) in 0.5MH2SO4.
3.32 In situ UV/Visible Spectroscopy
Fig. 3.26 (a) and (b) show the UV/Vis spectra of PANI and PANI/PVA film, deposited on ITO
coated glass electrode respectively. The various electrode potentials for both the samples are
ERHE = 0.0 to 0.8 V. In the absorption spectra of PANI the band at around λ= 315 nm is assigned
to the π−π* transition of the benzenoid segment of reduced PANI [115, 116]. This peak is shifted
to 360 nm in the spectra of PANI-Cu product. The band at λ= 420 nm in both PANI and PANI-
PVA having maximum intensity at ERHE = +0.3 V is related to an intermediate redox state of the
PANI film, which possibly possesses non conjugated benzenoid units in a polymer chain [115-
119]. The main absorbance band in the red region of the UV/Vis spectra of both PANI and
PANI/PVA is assigned to the emeraldine form of PANI. This peak is also shifted towards the
lower wavelength with increase in potential as reported earlier [119]. In PANI sample a decrease
in the intensity of the band at λ= 315 nm and a progressive increase in the intensity of the band in
the red region is observed by shifting the electrode potential to higher values, indicating a
decreasing number of benzenoid units and increasing number of quinoid units because of
oxidation of the leucoemeraldine into the emeraldine form of PANI. This behavior is more
prominent in PANI as compared to PANI/PVA product.
77
Figure 3.26. UV/Vis spectra of (a) PANI and (b) PANI/PVA film, deposited on ITO coated
glass electrode, obtained at different electrode potential values ranging from ESCE= 0.0 TO 0.8 V
at an interval of 0.1 V.
The dependence of absorbance on potential at different wavelengths i.e 315 nm, 420 nm, and 750
nm for PANI and 420 nm and 750 nm for PANI/PVA derived from Fig.3.26 (a) and (b) are
shown by the graph in Fig. 3.27 (a) and (b) respectively. In case of PANI a decrease in
absorbance at λ= 315 and 360 nm is observed by sweeping the potential to higher values which
78
is assigned to the conversion of benzenoid segments to quinoid segments of PANI [115]. The
absorbance maxima for the band at λ= 420 nm is observed at around ERHE = +0.3 V which is
assigned to the intermediates formed during the electro oxidation of leucoemeraldine form of
PANI [117-119]. A progressive increase in the absorbance band at λ= 750 nm with the increase
in potential indicates the increase in quinoid segments of emeraldine form of PANI [119].
Figure 3.27 (a) and (b) Absorbance vs. Potential at three selected wavelengths, derived from the
above displayed spectra in Fig 3.26. (a) and (b).
79
3.33 Results and Discussion (Part V)
3.34 Conductivity Measurements and Mass Yield
Table 3.10 shows the mass yield and conductivity measurements of PANI, PANI-Cu,
PANI-PVA, and PANI-Cu-PVA. The conductivity of the three component system i.e PANI-Cu-
PVA is greater than the conductivity of pure PANI, PANI-Cu, and PANI-PVA as shown by
Table 3.10. The conductivity of two component system comprising of PANI-Cu is less than the
conductivity of alone pure PANI and two component PANI-PVA system. The Cu particles
embedded in the PANI matrix are responsible for the decrease in conductivity of PANI-Cu
because they partially block the conductive path present in the neat PANI [105]. This is further
confirmed by the XRD data shown in Fig. 3.31 (b) where the crystallinity of PANI-Cu is less
than the rest of the samples.
Table 3.10. Mass Yield and Conductivity Measurements
Sample Mass yield (g) Conductivity(S/cm)
PANI 0.1947 1.92×10-2
PANI-Cu 0.0979 5.12×10-3
PANI-PVA 0.1423 6.65×10-2
PANI-Cu-PVA 0.1243 1.04×10-1
80
3.35 UV/Visible Spectroscopy
The UV/Vis spectra of PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA are shown in Fig.3.28
(a), (b), (c), and (d) respectively. The UV/Vis spectra of PANI [Fig. 3.28 (a)] and PANI-PVA
[Fig.3.28 (c)] show two peaks at around 330 nm and 640 nm which are assigned to the π−π*
transition of benzenoid and n−π* transition of quinoid units of polyaniline respectively [92]. In
case of PANI-Cu [Fig.3.28 (b)] the peak for the quinoid unit is shifted towards the lower
wavelength at around 560 nm which could be due to the presence of Cu II chromophores [107].
In case of the three components system i.e PANI-Cu-PVA [Fig.3.28 (d)] the peak for quinoid
unit appears at around 580 nm which is red shifted as compared to PANI-Cu and blue shifted as
compared to both PANI, and PANI-PVA. A shoulder peak at around 280 nm in both PANI-Cu
and PANI-Cu-PVA is also present which is indicative of the presence of Cu II [107]. This peak
at 280 nm is absent in both PANI and PANI-PVA.
Figure 3.28. UV/Vis spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
3.36 FTIR Spectroscopy
The FTIR spectra of PANI, PANI-Cu, PANI-PVA, and PANI-Cu-PVA is shown in Fig. 3.29 (a),
(b), (c), and (d) respectively. The benzenoid and quinoid unit of polyaniline are shown by the
81
peaks at around 1498 and 1582 cm-1. The C-N and C=N stretching modes are shown by the
bands at 1307 and 1230 cm-1 respectively [17]. The C-H in-plane and out-of-plane bending
modes are evident from the peaks at 1139 and 826 cm-1 respectively [17]. In case of PANI-Cu
the intensity of quinoid unit is more as compared to all other samples which indicates the
interaction of Cu with the nitrogen atom of imine units of polyaniline [108], however the
expected blue shift of the quinoid peak is not observed in our case which may be attributed to the
co- formation of Cu aniline complex [87] and low molar concentration of CuCl2 solution in the
reaction mixture. In case of PANI-PVA there is no significant change in the position and
intensity of peaks for the quinoid and benzenoid units of polyaniline, thus there is no chemical
interaction of PVA with PANI [123]. In case of three components PANI-Cu-PVA system, a
significant decrease is observed in the intensity of peaks for the amine and imine units of
polyaniline.
Figure 3.29. FTIR spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
3.37 Thermo gravimetric Analysis (TGA)
Thermo-gravimetric analysis was carried out to test the thermal stability of the synthesized
materials. The TGA curves for PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA are shown in
Fig. 3.30 (a), (b), (c), and (d) respectively. Fig. 3.30 shows that the loss in mass from 30 to 300
82
oC in the PANI-Cu, PANI-PVA and PANI-Cu-PVA is almost the same and less than that of neat
PANI. This loss in mass is attributed to the removal of water molecules from the polymer chain
[109]. From 300-400 oC a greater mass loss is observed in all the samples which is attributed to
the removal of acid dopants from the polymer structure [109]. The degradation of polymer chain
starts at even higher temperature for all the samples [109] and at 600oC the % mass loss for
PANI (98.56%) is greater than the % mass loss of the PANI-Cu (53.17%), PANI-PVA (67.94%)
and PANI-Cu-PVA (72.11%). This indicates that the thermal stability of the composites of PANI
is more than the neat PANI [107, 124].
Figure 3.30 TGA analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
3.38 X-Ray Diffraction
The XRD patterns of PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA are shown in Fig.3.31
(a), (b), (c) and (d) respectively. In comparison of PANI Fig.3.31 (a) and PANI-Cu, Fig.3.31 (b)
the characteristic peak for both appears at 2θ = 13o, 19o and 25o indicating that both the samples
are amorphous [16]. Since the XRD peaks for PANI-Cu are mostly similar to that of the free
PANI so this suggest that the structure of CuCl2 may be distorted during the process of
polymerization [110], moreover, the peaks for PANI sample are slightly sharper than PANI-Cu
83
which suggest that the PANI sample is more crystalline than PANI-Cu. This is consistent with
the conductivity data as discussed in table 3.10.
The PANI/PVA (Fig. 3.31 (c)) show the characteristic peak of PVA at 2θ=20o which confirms
the presence of PVA in PANI [124]. The PANI/PVA sample have peaks at 2θ=12o, 20o and 25o
showing the amorphous nature [16]. However, the peak at 2θ=25o is more intense in PANI/PVA
thus the crystallinity of PANI/PVA is more than PANI due to the insertion of PVA [10]. This is
supported by the fact that the conductivity of PANI-PVA has increased (see table 3.10) with the
increase in crystallinity.
Fig. 3.31 (d) shows the XRD pattern of PANI-Cu-PVA. In comparison the crystallinity of the
three component system PANI-Cu-PVA is less than PANI-PVA, comparable to neat PANI, and
greater than PANI-Cu. However, this observation is in contrast with the conductivity data
discussed in table 3.10 where the conductivity of the three component system is greater than any
of the other two component system and neat PANI itself.
Figure 3.31. XRD analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
84
3.39 SEM Analysis
Fig. 3.32 (a), (b), (c), and (d) shows the SEM images of PANI, PANI-Cu, PANI/PVA, and
PANI-Cu-PVA respectively. The surface morphology for PANI [Fig. 3.32 (a)] is un even and
irregular as reported in previous literature [57]. The PANI-Cu [Fig. 3.32 (b)] seems to be more
porous and irregular as compared to PANI [111]. The pore size in PANI-Cu is larger and uneven
as compared to PANI which leads to the change in morphological structure from firm gravel to
lose cotton appearance.
The SEM image of PANI/PVA [Fig.3.32 (c)] shows the presence of small granules of PVA in
the PANI matrix. The PANI/PVA composite show irregular shaped particles with variable size.
The non compatibility of two components is responsible for the irregular shape of PANI/PVA
composite [128]. Moreover, the PANI/PVA is more porous as compared to PANI [103, 129] and
PANI-Cu. In the PANI/PVA the sharp edges of particles can easily be correlated with the XRD
data as discussed in Fig 3.31 (c). The average particle size of PANI/PVA is 4μm.
Fig. 3.32 (d) shows the SEM image of the three component system PANI-Cu-PVA. The surface
of the three component system is smoother than PANI, PANI-Cu, and PANI-PVA. Similar
smooth morphology is reported for the three component system of PANI-PVA-NiO
nanocomposites [131].
85
Fig 3.32. SEM images of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
***********************
85
Fig 3.32. SEM images of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
***********************
85
Fig 3.32. SEM images of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.
***********************
86
4. CONCLUSION
The synthesis of polyaniline by using copper (II) chloride as oxidant was investigated in
detail. The UV/Vis, FTIR, XPS, NEXAFS and SSNMR and elemental analysis showed that
polyaniline was formed in a partially oxidized form, partially protonated with [CuCl3]- as the
dopant counter ion. The results of SEM show the spherical morphology of particles. A decrease
in the final pH of the reaction solution and an increase in the reaction yield with an increase in
the oxidant to monomer ratio were observed. The increase in the yield of the reaction was
ascribed to an increase in the oxidation potential of CuCl2 with an increase in its molar
concentration. The low yield of the reaction was attributed to the co-formation of a copper(II)
chloride aniline complex. Although the mass yield of reaction was on the low side (ca. 10% or
less), the present work indicates that weak oxidizing agents, such as copper(II) chloride can be
used for the oxidative polymerization of aniline. Oxidation of aniline by transition metal salts has
been proposed as a method for producing polyaniline/metal composites [83], and the production
of polyaniline/copper composites by using copper(II) compounds as the oxidant has been
proposed [84, 132]. However, it is apparent from the present work that, in the absence of air, a
significant amount of polymerization only occurs if a large excess of the copper(II) compound is
used. Moreover, the presence of copper metal in the product seems unlikely. For example, in a
recently reported study [132], the presence of copper as copper metal in the product appears to
have been assumed rather that proven, and the amount of “copper” found (46.6 wt. %) is
considerably greater than the theoretical maximum amount (39.4%) for the proposed mechanism
involving reduction of copper(II) to copper(0). These observations indicate that considerable care
is required to identify the exact nature of the reaction products before claiming the synthesis of a
particular polyaniline/metal composite.
In the present work we are not advocating the use of copper(II) chloride as a suitable
oxidant for the bulk synthesis of PANI, because it clearly is not. Rather, we have shown the kind
of reaction conditions and product characterization methods that are necessary to obtain well-
characterized PANI and to determine the true nature of the copper that is incorporated in the
product.
87
Polyaniline synthesis was carried out by using CuCl2 as oxidizing agent. The results
obtained from the FTIR, UV/Vis and elemental analysis show the presence of polyaniline in the
leucoemeraldine form. A decrease in pH of the reaction mixture with increase in oxidant:
monomer ratio was observed. Similarly an increase in the yield of reaction with increase in
oxidant : monomer ratio was observed which was attributed to the increase in oxidation potential
with increase in the molar concentration of copper II chloride. The formation of leucoemeraldine
was attributed to the low oxidation potential of CuCl2.
An inverse emulsion polymerization method was used to investigate the synthesis and
characterization of polyaniline doped with Cu II chloride. The results show that polyaniline was
coordinated with Cu II chloride. The TGA results show an increased thermal stability for PANI-
Cu while the XRD data proposed relatively less crystallinity of the composite. A decrease in
crystallinity causes the decrease in conductivity of the PANI-Cu composite. The cyclic
voltamograms indicate that the composite material (PANI-Cu) is electroactive. The SEM result
shows an uneven morphology for PANI-Cu composite with large pore size as compared to
PANI.
The synthesis and characterization of polyaniline doped with polyvinylalcohol was
investigated by inverse emulsion polymerization. The results show the presence of EB form of
polyaniline doped with polyvinylalcohol. The TGA and XRD results show an increased thermal
stability and better crystallinity of the composite PANI/PVA. An increase in conductivity was
observed as the crystallinity of composite increases. The composite material (PANI/PVA) was
found to be electroactive as clear from the cyclic voltamograms.
Polyaniline (PANI), polyaniline doped with polyvinylalcohol (PANI-PVA), polyaniline
doped with copper (PANI-Cu) as well as polyaniline co-doped with polyvinylalcohol and copper
(PANI-Cu-PVA) were prepared under similar conditions by inverse emulsion polymerization.
The UV/VIS and FTIR were used to examine the chemical structure of synthesized products.
The SEM results show the smooth morphology for the three component system of PANI-Cu-
PVA in comparison to PANI, PANI-Cu and PANI-PVA. The thermal stability of PANI-Cu-PVA
was found to be greater than PANI and less than PANI-Cu and PANI-PVA as shown by TGA.
The XRD data confirms the amorphous nature of all the samples.
88
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