Change in AC conduction mechanism together with conversion of submicron to nanoparticles in polyaniline and its poly(vinyl pyrrolidone) blends on heating-induced water elimination

Abstract

The present work is an investigation of AC impedance behaviors of polyaniline (PANI) and its poly(vinyl pyrrolidone) (PVP) blends. The materials were prepared by polymerization of aniline hydrochloride without/with PVP using FeCl 3 oxidant. PANI–PVP blends have greater AC conductivities than that of PANI in proportion to the amount of PVP incorporated. At lower frequencies (10 Hz – critical frequency f c) conductivity remains independent but at frequencies > f c, conductivity raises with frequency. In the entire range, however, the universal power law σ ac( ω) = Aω s holds good. In fresh condition PANI exhibits an increase in bulk resistance ( R b) and frequency exponent s up to 373 K and blends up to 423 K beyond which they show a decrease. The trend in conduction could be explained by the operation of small polaron tunneling up to 373/423 K and afterwards correlated barrier hopping (CBH) conduction mechanisms. Studied PANI, PANI–PVP blend materials and a fresh but annealed (463 K) PANI all display only a decrease in R b and s values in the entire temperature range of study and hence they follow only CBH mechanism. The fresh samples, together with change of conduction mechanism with temperature also undergo submicron to nanoparticles conversion and changes in other physico-chemical properties. All these changes have the origin on elimination of occluded water from the fresh materials on heating.