Effects of Residual Solvent on Membrane Structure and Gas Permeation in a Polymer of Intrinsic Microporosity: Insight from Atomistic Simulation

Microstructure and permeation in a polymer membrane are closely related to residual solvent during membrane fabrication. In this study, we conduct atomistic simulation to investigate the effects of residual solvent on free volume :, distribution and H-2 permeation in a polymer of intrinsic microporosity (PIM-1). The interaction energies of three solvents (CHCl3, CH3OH, and H2O) with PIM-1 are predicted to be -16.3, -9.6, and -7.0 kcal/mol, respectively, which are in good agreement with available experimental data. On this basis, a structure-property relationship is proposed between interaction energy and the critical volume of solvent. The cyano and dioxane groups in PIM-1 interact preferentially with CH3OH and H2O; however, the carbon atoms interact more strongly with CHCl3. The mobility of residual solvent is found to decrease in the order of H2O > CH3OH > CHCl3. Upon comparison, the mobility of PIM-1 chains is smaller but facilitated by solvent due to the cooperative interactions between polymer and solvent. The fractional free volumes and large-size voids in PIM-1/solvent membranes are observed to decrease as CH3OH > CHCl3 > H2O, consistent with positron annihilation lifetime spectroscopy measurements. The solubility and diffusion coefficients of H-2 decrease in the same hierarchy, and the predicted and experimental coefficients are in fairly good agreement. This simulation study provides atomistic insight into the microscopic properties of residual solvent in a polymer membrane and reveal.; the crucial role of residual solvent in tailoring membrane structure and gas permeation.