Molecular Understanding of Polyaniline in Imidazolium based Ionic-Liquid and Water Mixtures: A Molecular Dynamics Simulation Study.

Monitoring of the interactive influence of cations and anions is inevitable for the development of conductive membranes using polyaniline (PANI). In this paper, EB (emeraldine base) and ES (emeraldine salt) forms of PANI structural properties were understood in different imidazolium ionic liquid-water mixtures using molecular dynamics simulations.  We calculate the conformational and structural properties of PANI using the combinations of two cations (1-ethyl-3-methylimidazolium [EMIM]+ and 1-butyl-3-methylimidazolium [BMIM]+) and five anions (acetate [ACT]-, formate [FRM]-, trifluoromethyl-sulfonate [TFS]-, benzoate [BEZ]-, and nitrate [NO3]-). Based on various structural properties, it is understood that the anions play a dominant interactions with EB or ES compared to cations. Interestingly, we observe that the radius of gyration shows an increase with [BMIM]+ and a decrease with [EMIM]+ with respect to the increasing size of the anion. There is a decrease in van der Waals interaction for ES due to the elongation of the chain when compared to EB. The excess molar volume shows more solvation behaviour for ES than EB. Nevertheless, increase in anion size leads to the favourable solvation of EB and ES. These observations help in the selection of the best combination of ILs for the sustainable designing of polymer membranes and their applications.