Effects of the matrix molecular weight on conductivity and dielectric relaxation in plasticized polyaniline/polymethylmethacrylathe blends

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.