Molecular Dynamics Simulation Study on the Structural and Thermodynamic Analysis of Oxidized and Unoxidized Forms of Polyaniline

The conducting polymer polyaniline (PANI) has shown significant interest for the development of electrified membranes (EMs) with superior antifouling characteristics. However, the blending and doping of PANI with other polymers and nanomaterials highly influence the properties of the membrane surface. PANI exists in two forms: oxidized, known as emeraldine salt (ES), and unoxidized, referred to as emeraldine base (EB). Therefore, understanding the different forms of PANI and the variations between the oxidized and unoxidized forms along the length of the polymer chain is intriguing. In this paper, we present the design of a novel copolymer consisting of EB and ES monomers with varying charge densities and different segmental arrangements. We present various intra- and intermolecular structural properties of the PANI chains using all-atom molecular dynamics (MD) simulations. Herein, we present a detailed conformational free energy analysis to understand the conformational transitions of the PANI chains. Our results show increased radius of gyration (Rg) values with increased charge density. Furthermore, we also present the H-bonding, free energy analysis, reduced density gradient (RDG), and solvent-accessible surface area (SASA) values for the observed conformational transitions of PANI. Therefore, these observations are crucial in understanding the complex behavior of chains for designing target-specific polymeric materials.