Effects of residual solvent on membrane structure and gas permeation in a polymer of intrinsic microporosity: Insight from atomistic simulation

Abstract

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 (CHCl 3, CH 3OH, andH 2O) 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 CH 3OH and H 2O; however, the carbon atoms interact more strongly with CHCl 3. The mobility of residual solvent is found to decrease in the order of H 2O > CH 3OH > CHCl 3. 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 CH 3OH > CHCl 3 > H 2O, 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 reveals the crucial role of residual solvent in tailoring membrane structure and gas permeation.