(628c) Atomistic Investigation of CO2-Induced Plasticization in PIM-1 Polymer

Membrane plasticization has been a major concern over years in the industrial application of gas separation membranes. At elevated gas pressures, condensable gases such as CO₂, induce swelling of polymeric membranes resulting reduced selectivity hence loss of separation performance. Prediction of the plasticization pressure requires elaborate high-pressure experiments. While molecular simulation is a powerful tool to predict materials performances, modelling gas separation performances of polymeric structures is proven to be challenging due to the complex and flexible structures. In this work, CO₂-induced plasticization of promising PIM-1 membranes were investigated using a complete molecular simulation approach.

A detailed study on modeling of PIM-1 was accomplished for accurate simulations of the material to be performed. Quantum-level charge calculations were integrated wih all-atom force fields for PIM-1 model. Molecular Dynamics (MD) and Monte-Carlo (MC) simulations were integrated in order to mimic PIM-1 chain behaviors with and without CO2 presence and also CO₂ sorption on the membrane. The methodology was validated in previous studies [1], where plasticization pressure of several polyimides were predicted. CO₂ sorption simulations up to 40 bar were carried out using integrated MD-MC simulation and validated using experimental data.

Plasticizing effect of CO₂ was then investigated using specific fractional free volume (FFV) analysis that evaluates interconnected CO₂-accessible free volume. Experimental physical properties of PIM-1 such as density, FFV and glass transition temperature, were successfully reproduced via simulations. Accurate modeling of rigid PIM-1 chains were accomplished and structural analyses on plasticization were performed.

This work was supported by the Scientific and Technological Research Council of Turkey - TUBITAK (Grant# 217M630) ) and the Scientific Projects Unit of Istanbul Technical University (Grant# MDK-2018-41400).

[1] Balcik M., Ahunbay M.G., Prediction of CO2-induced plasticization pressure in

polyimides via atomistic simulations, J. Memb. Sci. 547 (2017) 146-155.