Interfacial analysis of mixed-matrix membranes under exposure to high-pressure CO₂

Mixed-matrix membranes (MMMs), combining mechanical/separation properties and processability of different materials, have been considered as promising materials in tackling challenging gas separation problems such as carbon dioxide/methane separation. In this study, a detailed atomistic investigation of Matrimid®/ZIF-8 MMM was carried out to understand the evolution of the interfacial dynamics due to plasticization when exposed to high-pressure CO₂. For the analyses, a three-dimensional interface was modelled representing a ZIF-8 nanoparticle embedded in a Matrimid® matrix. Simulations confirmed chain rigidification of the polymer near the ZIF-8 surface. An analysis of the effect of CO₂ sorption on the interface indicated that, while the interface had no significant effect on the sorption behavior up to 10 bar CO₂ pressure, it emerges as the dominant sorption site at higher pressures. This study revealed two new phenomena: (1) the loading of gas molecules at the interfacial region resulted in expansion of the interface providing more space for additional CO₂ sorption; and (2) the de-rigidification of previously rigidified chains in the presence of CO₂. These phenomena may be the key factors in characterizing mixed gas separation performance.