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 H2 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 H2 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.

Effect of methanol treatment on gas sorption and transport behavior of intrinsically microporous polyimide membranes incorporating Tröger׳s base

“…Previously, the solubility coefficient was calculated from permeability and diffusivity data measured by time-lag analysis [34]. In addition, the effect of residual solvent on the change of gas separation behavior was investigated by atomistic simulation [35]. In the present study, we evaluated the gas permeability, diffusivity, and solubility of PI-TB membranes for small gas molecules in order to improve the understanding of gas transport properties by applying a solution-diffusion model.…”

Polymers of Intrinsic Microporosity

“…The application of packing simulation to understand and predict the performance of PIMs as gas separation membranes (see below) is also an active area of research [100][101][102]. However, it should be noted that, at present, simulations of PIM packing do not take into account polymer dynamics, which are important for the accurate prediction of gas diffusivities, nor do they give information on possible swelling effects due to gas adsorption.…”

Interaction of a Polymer of Intrinsic Microporosity (PIM-1) with Penetrants

“…A PIM-1 film cast from CHCl 3 , for example, has been known to behave differently to a film of the same material cast from THF. The influence of these interactions has been analysed for various polymers, including polyetherimides [5] and perfluorinated polymers [7], as well as PIM-1 [8] and carboxylated analogues of PIM-1 [9] Dipole-dipole interactions and hydrogen bonding have been identified as possible contributors to changes in transport properties; the latter being especially prevalent in polymers where there are ether connector groups present.…”

“…For PIM-1, the effect of residual solvent has been studied both experimentally [5] and computationally [8] In both cases the ether linkage and the nitrile group were identified as likely sites for interaction with residual solvents (encompassing casting solvents, lower alcohols and nonsolvents). This paper reports techniques used to investigate (1) the dependence of PIM-1 solubility on molar mass, (2) the effect that lower alcohols, so called residual solvents and water have on the free volume in PIM-1 and (3) on the interaction sites in the polymer.…”