Polyaniline-water interactions: A theoretical investigation with the polarisable continuum model

The simulations of emeraldine hydrochloride tetramers were performed for the first time in implicit water solvent using the polarisable continuum model (PCM) with the density functional theory (DFT) method. This approach should be more appropriate for the study of the conducting form of polyaniline as all known processes of synthesis and further transformations take place in polar medium. Our results confirm this hypothesis and clearly indicate that the geometry and electronic structure of the emeraldine salt depend on the dielectric properties of the medium. In polar environment the protons are bound tighter to the chains compared to vacuum and this leads to stronger impact of the dopant on the structural parameters of PANI. As a consequence, the density distribution in the emeraldine hydrochloride obtained by PCM is more realistic compared to vacuum estimates. The stability in polar. medium of two possible salt configurations with respect to counterions position is assessed. Each configuration is simulated in singlet and triplet state (bipolaron and polaron). The results show that at the tetramer level the bipolaron form is always preferred in accordance to available experimental results. (C) 2010 Elsevier B.V. All rights reserved.