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

Abstract

Monitoring interactive influence of cations and anions is inevitable for the development of conductive membranes using polyaniline (PANI). Herein, emeraldine base (EB) and emeraldine salt (ES) forms of PANI structural properties are understood in different imidazolium ionic liquid–water mixtures using molecular dynamics (MD) simulations. 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]⁻) are calculated. Based on various structural properties, it is understood that the anions play a dominant interaction with EB or ES compared to cations. Interestingly, it is observed 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 behavior for ES than EB. Nevertheless, an increase in anion size leads to the favorable 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.