Effects of Imidazolium‐Based Ionic Liquids on Molecular Structural Transitions of Polysulfone Using Molecular Dynamics Simulations

Polysulfone (PSF)‐ionic liquids (ILs) composites exhibit great potential for the development of advanced ultrafiltration membranes. Therefore, understanding the molecular‐level interactions between PSF and IL is critical. In this work, the structure and intermolecular properties of PSF with two cations, 1‐butyl‐3‐methylimidazolium (BMIM + ) and 1‐ethyl‐3‐methylimidazolium (EMIM + ) with a combination of six anions (NO 3 − , FRM − , ACT − , BF 4 − , TFS − , and BEZ − are studied using molecular dynamics simulations. The conformational structures of the PSF chains are analyzed using the radius of gyration ( R g ), which increases with increasing anion size. Radial distribution functions present strong PSF–ion interactions for EMIM + . Spatial distribution functions reveal the anion clustering around the PSF monomers for small anions compared to large anions. Reduced density gradient presents a combination of both van der Waals and steric repulsions for both large and small anions. Excess molar volume () and solvent‐accessible surface area capture the structural properties of the polymer and its favorable interactions with the ILs as anion size increases. The self‐diffusion coefficients of ILs show minimal effect in the presence of PSF other than BF 4 − . Overall, the results provide a systematic framework of how anion‐cation combinations regulate the polymer structure and interactions in the environment.