(371g) Role of Solvent in Structural Reorganization of a Polymer Membrane: An Atomistic Simulation Study

The swelling of a polymer membrane in a solvent plays a significant role in the reorganization of the polymer chains, as well as the membrane performance for organic solvent nanofiltration (OSN). In this work, an atomistic simulation study is reported on the structural characteristics (accessible pores, pore size distribution and polymer mobility) for a polybenzimidazole (PBI) membrane swollen in three different solvents, including water, methanol and ethanol. The swelling degrees of the PBI membrane in water (7.85%), methanol (15.50%) and ethanol (17.20%) are obtained from reported experimental measurements. The simulation results indicate that the reorganization of polymer chains is mainly determined by the polarity of solvents, the hydrophobicity of polymer, and the competition of solvent-polymer and polymer-polymer interactions. Due to the higher capability of ethanol for PBI swelling, the pore size of the membrane swollen in ethanol is larger than swollen in other two solvents (methanol and water). Furthermore, acetone flux and solute rejection in three swollen membranes are estimated from simulation and it is found that the membrane swollen in ethanol shows a better performance than in the other two solvents. This simulation study provides microscopic insight into the reorganization of polymer chains in the PBI membrane, and suggests that the membrane structure and performance can be subtly tuned by varying the pre-treated solvents.