Molecular Dynamics\nSimulation Study on the Structural\nand Thermodynamic Analysis of Oxidized and Unoxidized Forms of Polyaniline

The conducting polymer polyaniline (PANI) has shown significant\ninterest for the development of electrified membranes (EMs) with superior\nantifouling characteristics. However, the blending and doping of PANI\nwith other polymers and nanomaterials highly influence the properties\nof the membrane surface. PANI exists in two forms: oxidized, known\nas emeraldine salt (ES), and unoxidized, referred to as emeraldine\nbase (EB). Therefore, understanding the different forms of PANI and\nthe variations between the oxidized and unoxidized forms along the\nlength of the polymer chain is intriguing. In this paper, we present\nthe design of a novel copolymer consisting of EB and ES monomers with\nvarying charge densities and different segmental arrangements. We\npresent various intra- and intermolecular structural properties of\nthe PANI chains using all-atom molecular dynamics (MD) simulations.\nHerein, we present a detailed conformational free energy analysis\nto understand the conformational transitions of the PANI chains. Our\nresults show increased radius of gyration (<i>R</i><sub>g</sub>) values with increased charge density. Furthermore, we also\npresent the H-bonding, free energy analysis, reduced density gradient\n(RDG), and solvent-accessible surface area (SASA) values for the observed\nconformational transitions of PANI. Therefore, these observations\nare crucial in understanding the complex behavior of chains for designing\ntarget-specific polymeric materials.