Microscopic and macroscopic transport properties of polyaniline: effect of chain orientation and hydration

Summary form only given. While it is well-known that stretch-orientation of a conducting polymer film induces an anisotropy of the macroscopic DC conductivity, very few is known about the effects on the transport at microscopic scale. We present a comprehensive study of transport anisotropy at both scales, in a set of stretched and unstretched polyaniline films. From spin dynamics techniques, mainly proton spin lattice relaxation time measurements as a function of frequency, it is evidenced that polaron motion is a highly anisotropic quasi 1-D diffusion in all the samples. It is shown that while stretching increases parallel DC conductivity it favours inter-chain hopping at the microscopic scale. Besides, the effect of hydration on transport anisotropy at both scales has been investigated too. It appears that the increase of DC conductivity goes together with a decrease of the macroscopic anisotropy. At the chain level, a stong increase of the inter-chain hopping rate is observed. All the results can be -interpreted in coherent picture that links the macroscopic properties to the microscopic ones. In this picture, DC conductivity anisotropy is shown to be governed by geometrical parameters provided that the microscopic anisotropy is very high.