We report the results of spectral, structural and electrical investigations on plasticized polyaniline/polymethylmethacrylate blend films (PAni/PMMA), obtained by the co-dissolution method using three different molecular weights of the PMMA matrix. The use of dibuthylphtalate as a plasticizer allowed us to obtain free standing thin films. The system showed percolation behaviour with an extremely low percolation threshold, independently of the PMMA molecular weight. The ac conductivity is well described by the universal Jonscher's law. By using the dielectric modulus, we have observed a dielectric relaxation assigned to the hopping of charge carriers (polarons and bipolarons) between localized states. The characteristic frequency of this relaxation follows an Arrhenius law and the activation energy depends on the PMMA molecular weight. This relaxation is well described by a simple Debye process for the lowest PMMA molecular weight and deviates from this model when the molecular weight of the PMMA increases.

We report the results of studies on two series of polyaniline (PANI), doped with dichloroacetic (DCA) and trichloroacetic (TCA) acids, respectively, at various doping rates and obtained by the in situ polymerization method. Samples were characterized by x-ray diffraction, scanning electron microscopy and conductivity measurements. The direct current (dc) and alternating current (ac) electrical conductivities of PANI salts have been investigated in the temperature range 100–310 K and frequency range 7–106 Hz. The results of this study indicate better chain ordering and higher conductivity for PANI doped with TCA. The dc conductivity of all samples is suitably fitted to Mott’s three-dimensional variable-range hopping (VRH) model. Different Mott parameters such as characteristic temperature T0, density of states at the Fermi level (N(EF)), average hopping energy (W) and the average hopping distance (R) have been evaluated. The dependence of such values on the dopant acid used is discussed. At high frequencies, the ac conductivity follows the power law σac(ω,T) = A(T)ωs(T,ω), which is characteristic for charge transport in disordered materials by hopping or tunnelling processes. The observed increase in the frequency exponent s with temperature suggests that the small-polaron tunnelling model best describes the dominant ac conduction mechanism. A direct correlation between conductivity, structure and morphology was obtained in our systems.

We report the results of dielectric measurements over the frequency range10 Hz–1 MHz and the temperature range 150–300 K on polyaniline subjected to doping with dichloroacetic acid (DCA) and trichloroacetic acid (TCA) with various doping levels (6.1%, 8.2%, 13.3% and 4.1%, 6.15%, 13.5%, respectively). Conductivity is increased when the doping level or temperature is increased and samples doped with TCA are more conductive than those doped with DCA. A high frequency relaxation peak is observed in the loss factor curves attributed to the motion of charge carriers in the bulk polymer. A second loss peak appears in the low frequency range when we use the dielectric modulus representation and is attributed to electrode polarization. Both relaxations are well fitted by the Havriliak–Negami function, and the fitting parameters are determined. The characteristic relaxation frequency is described by the Arrhenius law. The activation energy for both relaxations is decreased by increasing the doping level and it is lower in the case of TCA doping acid.

The effects of the molar mass of polymethylmethacrylate (PMMA) on electrical, structural and morphological properties of conductive polyaniline-polymethylmethacrylate blends have been studied. We have plasticized the PMMA matrix by using dioctyl phthalate (DioPh). Three different molar masses of PMMA, 15 000, 120 000 and 350 000 g mol −1 , have been used. The x-ray diffraction analysis showed amorphous structure for all our studied PANI-PMMA blend films. The SEM micrographs showed more aggregation with the lowest molar mass of PMMA matrix. The direct current (dc) and alternating current (ac) electrical conductivities have been investigated in the temperature range 20-300 K and frequency range 7-1 × 10 8 Hz. The results of this study indicate an increase of the conductivity when the molar mass of PMMA decreases. With the lowest molar mass of PMMA (15 000 g mol −1 ), we obtained the lowest percolation threshold ( p c ≈ 0.3%). The dc conductivity is governed by Mott's three-dimensional variable range hopping (3D VRH) model; different Mott's parameters have been evaluated. At high frequencies, the ac conductivity follows the power law σ (ω, T ) = A(T )ω s (T,ω) , which is characteristic for charge transport in disordered materials by hopping or tunnelling processes. The observed decrease in the frequency exponent s with increasing temperature suggests that the correlated barrier hopping (CBH) model best describes the ac conduction mechanism. All our blends are well described by the scaling law σ (ω)/σ dc = 1 + (ω/ω c ) n with n ≈ 0.51-0.52.

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