Effects of the molar mass of the matrix on electrical properties, structure and morphologyof plasticized PANI–PMMA blends

Abstract

The effects of the molar mass of polymethylmethacrylate (PMMA) on electrical, structuraland morphological properties of conductive polyaniline–polymethylmethacrylateblends have been studied. We have plasticized the PMMA matrix by using dioctylphthalate (DioPh). Three different molar masses of PMMA, 15 000, 120 000 and350 000 g mol−1, have been used. The x-ray diffraction analysis showed amorphous structure for all our studiedPANI–PMMA blend films. The SEM micrographs showed more aggregation with the lowestmolar mass of PMMA matrix. The direct current (dc) and alternating current (ac) electricalconductivities have been investigated in the temperature range 20–300 K and frequency range7–1 × 108 Hz. The results of this study indicate an increase of the conductivity whenthe molar mass of PMMA decreases. With the lowest molar mass of PMMA(15 000 g mol−1), we obtained the lowest percolation threshold(pc≈0.3%). The dc conductivity is governed by Mott’s three-dimensional variablerange hopping (3D VRH) model; different Mott’s parameters have beenevaluated. At high frequencies, the ac conductivity follows the power lawσ(ω,T) = A(T)ωs(T,ω), which is characteristic for charge transport in disordered materials by hoppingor tunnelling processes. The observed decrease in the frequency exponents with increasing temperature suggests that the correlated barrier hopping (CBH) model bestdescribes the ac conduction mechanism. All our blends are well described by the scaling lawσ(ω)/σdc = 1+(ω/ωc)n with n≈0.51–0.52.