Direct analysis of lamellar structure in polyaniline protonated with plasticizing dopants

Abstract

Structural disorder in polyaniline (PANI) protonated with plasticizing dopants, namely diesters of 4-sulfophthalic acid containing linear alkyl or alkoxy subsituents (so-called plastdopants), has been investigated by both wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) measurements. Based on the experimental data we propose, in all cases studied, a lamellar-like structure in which a bilayer of plastdopant anions alternates with a layer of PANI chains. In order to account for the shape of the diffraction profiles obtained experimentally, we use a model in which statistical fluctuations of the electronic density are introduced along the stacking direction of the lamellae. The model enables us to calculate several structural parameters and in particular the average number of stacked layers constituting a crystallite. We also demonstrate that the disorder is principally governed by the structural features of the plastdopant bilayer. In particular strong interdigitation of long alkyl (alkoxy) tails of the plastdopant anions favors the formation of more ordered supramolecular domains.