185Interaction of components and conductivity in polyaniline – polymethylmethacrylate nanocomposites

© 2010 Advanced Study Center Co. Ltd.

Rev.Adv.Mater.Sci. 23(2010) 185-188

Corresponding author: O. Konopelnyk, e-mail: konopel@ukr.net

INTERACTION OF COMPONENTS AND CONDUCTIVITY INPOLYANILINE – POLYMETHYLMETHACRYLATE

NANOCOMPOSITES

���������� ���������������������������������������������������

������������ �!��"�����#��

���������������� ���������������������������������������������������������� �!�� �"�������������������#��$�� % ��&���'(�����)�% ���#��$�� % ��*����+��,�����

&�����������-�%(����$�%(�������� .��,�����

Received: December 20, 2009

Abstract. Polymer nanocomposites of poly(methyl methacrylate) (PMMA) with the conductingpolymer – polyaniline (PANI) were prepared by blending polymer solutions in a mixed organicsolvent. It is found that electrical conductivity of PMMA-PANI composites depends on the PANIvolume content with an extremely low “percolation threshold” near the 1.0% of the PANI. In theconcentration interval of 2-10 vol.% of PANI a specific conductivity exceeding one for acid dopedPANI is observed in PMMA-PANI composites. Introducing a conducting polymer into a dielectricPMMA matrix slightly decreases the glass transition temperature, causing the flow temperatureto rise significantly. It has been suggested that the increasing conductivity in PMMA-PANI com-posites is caused by an interaction of PANI nitrogen atoms with the functional groups of PMMAleading to additional doping of PANI.

1. INTRODUCTION

Polymer nanocomposites based on a conductingand insulating polymer matrix are a promising newgeneration of functional materials to be used inelectrooptical and sensor devices – flexible displays,panels, organic light emitting diodes, sensitive filmsfor environment monitoring [1,2]. In this aspect, ac-tive investigations are carried out for compositesbased on conducting polymers (polypyrrole,polythiophene, poly(phenylene vinylene), polyaniline)embedded in a dielectric matrix of polyvinyl alco-hol, polyvinyl chloride, polycarbonate and otherspolymers [3-6].

Such conducting polymers as polyaniline (PANI)have received a great attention due to their simplesynthesis, good environmental stability and electri-cal conductivity. The PANI may be considered as a

mesoscopic metal (a “nanometal“) with primary par-ticle diameters in the range between 10 and 20 nm[4]. However, major problems relating to successfulutilization of the PANI are poor mechanical propertyand low solubility in aqueous and organic solvents.Blending with such thermoplastic polymers as thepolymethylmethacrylate (PMMA) is employed toimprove the mechanical property and processabilityof the PANI [4,6]. The PMMA is chosen as dielec-tric matrix due to its high transparent ability in vis-ible spectral range which is important for optoelec-tronics, sensors and “smart window” applications[7].

It is known that the nanosize of polymer par-ticles is preserved in the polymer composites ob-tained by nanotechnology methods (template andmatrix synthesis, polymer blending in a co-solvent,

186 O. Aksimentyeva, O. Konopelnyk, I. Opaynych, B.Tsizh, A.Ukrainets, Y. Ulansky and G. Martyniuk

PANI content,vol.% 0 1 2 4 10 20 100

σ293

,Ohm-1.m-1 10-14 7.03.10-6 8.12.10-5 5.28.10-5 2.76.10-5 2.16.10-6 3.6.10-7

Table 1. Effect of the PANI content on the specific conductivity of PMMA-PANI nanocomposites.

PANI content, Glass transition Flow temperature, Microhardness,

wt.% temperature, T

g, K T

f, K F∞

.10-8, N/m2

0 383 412 2.05±0.10 1 381 414 1.87±0.10 2 379 420 1.88±0.10 4 382 425 1.81±0.1010 384 428 1.83±0.10

Table 2. Microhardness and thermomechanic characteristics of PMMA-PANI nanocomposites.

self-assembling, “in situ” polymerization, etc) [3,8].The mechanism of electron transport in suchnanosystems is a topic of great interest [4-6].

We have studied the electrical,thermomechanical properties and molecular struc-ture of polymer nanocomposites obtained by PANIand PMMA blending in their dilute solution in a mixedco-solvent.

2. EXPERIMENTAL

The dispersion of PANI doped by sulphuric acid wasprepared by oxidative polymerization of aniline(Aldrich) with ammonium persulphate (“CP” grade)in a 0.5 M sulphuric acid solution according to [9].The specific density of PANI doped with sulphuricacid was 1.224 g/cm3, the specific volume conduc-tivity measured at room temperature σ

293 = 3.6.10-7

Ohm-1.m-1. The dielectric PMMA matrix with a mo-lecular mass of 600000 mol/g characterised byglass transition temperature T

g = 383K, tempera-

ture of destruction TD = 473K. The PANI-PMMA

composites were prepared by blending a PANI andPMMA solution in a mixed toluene – dimethylsulphoxide - chloroform solvent under ultrasonictreatment for 24 hours. The solvent was evaporatedin dynamic vacuum conditions at T = 323K over 3days.

The samples for conductivity investigations wereprepared by pressing the PANI-PMMA compositesin cylinder bulk samples (d = 1.8 mm, h = 2 mm) atthe power of 150 atmospheres at T = 353K. Theelectrical conductivity of the PMMA-PANI compos-ites was measured by the two-probe method at room

temperature in the air. The thermomechanical curveswere obtained in the conditions of uniaxial compres-sion of the cylinder samples (d = 8 mm, h = 8-11mm) under simultaneous heating with the rate of 2grad/min [10]. The microhardness of composites wasmeasured by a Heppler consistometer as a limitedpoint of fluidity (F∞

., N/m2) at the characteristic power[10]. The Raman spectra of composites were ob-tained on a T64000 spectrometer, (Ar laser 514.5nm) at room temperature.

3. RESULTS AND DISCUSSION

It is believed that PANI-PMMA composites are acolloidal dispersion of polyaniline [6,8] inside aPMMA host matrix. It is found that the electricalconductivity in such polymer composites can becontrolled in a wide range (more than 8-10 orders ofmagnitude) by a small amount of PANI (Table 1).The nature of the conductivity dependence on thePANI content is very similar to the percolation shapefor blend polyvinyl chloride/polyaniline doped withcamphorsulfonic acid [6] with an extremely low “per-colation threshold” in the range of 0.8 – 1.0 vol.% ofPANI. When the PANI content becomes higher than2 vol.%, the σ values of PMMA-PANI compositesdecrease only slightly, while between 10 and 20vol.% of PANI σ decreases by almost one order ofmagnitude (see Table 1). Such behavior of the con-ductivity may be explained by the decreasing me-chanical strength of the composites, confirmed bytheir decreasing microhardness (Table 2).

We have suggested that an extremely lowthreshold of percolation for the PMMA-PANI com-

187Interaction of components and conductivity in polyaniline – polymethylmethacrylate nanocomposites

Fig. 1. Temperature dependence of relative defor-mation for PMMA-PANI composites at different PANIcontent.

Fig. 2. Raman spectra of PMMA-PANI nanocomposites.

posites is due to the formation of a conducting net-work in the dielectric matrix inside the host poly-mer [9]. On the other hand, a dielectric polymermatrix may affect the conjugated polymer’s elec-tron structure and change the population of unpairedspins corresponding to the concentration of polaroncarriers [5]. When the PANI concentration is higherthan 2 vol.% the value of specific conductivity inPMMA-PANI composites exceeds one for aciddoped PANI without a PMMA matrix (Table 1).

As shown by B. Wessing and collaborators [4]the conductivity in thermo-pressed composites ofPANI doped by d,l-camphor sulfonic acid (CSA) withPMMA containing 40% PANI(CSA), may be higherin comparison with unblended PANI(CSA). As sug-gested, a probable reason for such a phenomenonmay be additional doping of PANI by functionalgroups of PMMA near the melting temperature.

The effect of conducting polymer nanoparticleson the properties of a dielectric polymer matrix,

especially on its thermomechanical characteristicshas not been studied extensively. It is the effect ofinorganic fillers (nanoglay, nanotubes, colloidalsilica) on the glass transition temperature (T

g) of

polymer nanocomposites that has been most oftendescribed in the recent literature [8]. Taking intoaccount the low “percolation threshold” in the ob-tained PMMA-PANI composites their mechanicaland thermomochanical properties have been stud-ied at the PANI content of 1-10 vol.%.

A glass transition of a polymer will be affectedby its environment when the chain is within severalnanometers of another phase [8]. As can be seenin Fig. 1, an overall shape of the thermomechaniccurves for PMMA and composites at different PANIcontent is similar.

The effect of PANI nanoparticles on the PMMAmatrix consists in a decrease of the glass transi-tion temperature (T

g) from 1 to 4K at a low PANI

content (Table 2) and an increase at higher content.

188 O. Aksimentyeva, O. Konopelnyk, I. Opaynych, B.Tsizh, A.Ukrainets, Y. Ulansky and G. Martyniuk

Both the increases and decreases in Tg have been

caused by an interaction between the matrix andthe particles [8,11]. As a result of such interactionsome decrease in the microhardness of compos-ites (F∞ changes from 2.05.108 to 1.83. 108 N/m2) isobserved (Table 2). Such changes are in good cor-relation with the concentration dependence of theglass transition temperature for PMMA-PANI com-posites (Table 2).

The flow temperature for PMMA-PANI compos-ites arises significantly with the increasing PANIcontent compared to the free PMMA matrix (Fig. 1,Table 2). The PANI in the studied composites actsprobably as an “active” filler interacting with PMMAmacrochains at ambient temperature which leadsto a higher flow temperature of composites in com-parison with unblended PMMA.

The Raman spectra of composites obtained at adifferent PANI content are presented in Fig. 2. Ithas been shown that significant changes are ob-served in the bands corresponding to the nitrogenatom in the PANI macrochain (2500-3500 cm-1) andester oxygen attributed to PMMA (1270-1200 cm-1

and 2180 cm-1) as the PANI content in compositesincreases. Hence, these data confirm that the in-teraction between functional groups of conductingand insulating polymers proceeds in PMMA-PANIcomposites. Such interaction may be the reasonfor additional doping of PANI.

It is known that polyaniline achieves a high con-ductivity mainly in case of strong proton acids usedas doping agents [11]. In this polymer positive po-larons (cation-radicals) are considered as probablecharge carriers. The unpaired spins are localizedon the nitrogen atoms and the positive charge isdelocalized along a conjugated pi- electron systemof a polymer backbone [12]. It has been found inthe ESR investigation [5,9] that a PMMA matrix hasa significant influence on the linewidth (∆H

pp) of the

ESR signal: it broadens from 3.5 Oe (PANI) to 8.3Oe (PMMA-10%PANI). This confirms stronger de-localization of the charge carriers in PANI affectedby the PMMA dielectric polymer matrix of whichmay be one of the probable reasons for increasingthe composites’ conductivity.

On the other hand, the increase in the conduc-tivity in PMMA-PANI composites may be causedby “secondary doping” of primary acid doped PANI[12]. Such doping leads to a change in themacrochain conformation of PANI from a “compactcoil” to an “extended coil” as it proceeds under theinfluence some solvents (m-cresol, N,N-methylpyrrolidone) in PANI (CSA) [12]. It is believed that“secondary” doping conductivity in PMMA—PANI

blends causing the PANI coil conformation straight-ening would have such an effect.

4. CONCLUSION

The obtained results make it possible to suggestthat an interaction of components proceeds in theprocess of formation of composites and becomessignificant at ambient temperature in polymer com-posites based on a PMMA dielectric matrix and aPANI conducting polymer. A strong interaction ofPANI nanoparticles with PMMA macrochains resultsin increasing the composite flow temperature from412 to 428K. This effect is probably connected withsome additional doping of the PANI imine nitrogenby the PMMA ester functional group. Such dopingleads to higher electrical conductivity in the com-posite as compared with unblended PANI. Accord-ing to the results of thermomechanical measure-ments the obtained composites are conductive andsuitable for thermoplastic processing that may beused for producing antistatic screens, elements forelectronics, etc.

REFERENCES

/�0�12���%�������32���%���������42�5%(���%��66

����������� �����$%�7���+8�&���2

/�0��2�����9$9%(���:2�5��!��������;2�<�����66

������������ �����������%$�7���&8�+�2

/&0�-2���9��#2�'(�����������#2�'(9�66�����������

�����&�7���&8��2

/+0�1�<����������-2<2� ����=����>2�3��$��=���

<2?2�#(�������#2�"�����$�66�����������

������'�7����8���&2

/�0�52��2�:���!���������52��2�����@�������?2�?2

;9�����>2�?2�������9������?2�:2<(�@�������66

������������������������$(&�7����8�&��2

/�0�A2� �!� ���32���B�������:2�4��� �!��66�����

���������&�7����8����2

/�0�2�'�@������12�1�2�3�����66��������������

������������&�7����8����2

/*0�1232�,�9�������2�2�3�B�����66���������$%

7���*8�&�*�2

/�0�52��2�:���!���������#2�32�-�� (��52��2

����@�������:2�2�����������?2�:2�<(�@�������

��������!������ �����%(����$����7����8

���2

/��0�:2�2�����������52�2�:���!���������52�2

����@�������>2?2�������������52�2

;��%(9��66�!������"���"��� ���������

7���+8��&�2

/��0�:2���%1��!���66������� �����������

7����8����2

/��0�:2>2���%1��!�������:2C2�4@�(�����66�������

�������(%�7����8�*�2