Physical Gels of a Room Temperature Ionic Liquid: Mechanical Properties and Their Implications for Membrane Gas Separation

Physical gelation of room temperature ionic liquids (RTILs) using low molecular weight organic gelators (LMOGs) is an attractive approach to impart solid-like mechanical robustness to RTILs while maintaining high liquid-like permselectivity that makes RTILs attractive for gas separation. RTIL-based membranes in the current state-of-the-art supported ionic liquid membrane (SILM) format, fabricated by impregnation of porous supports, have commercially unattractive low gas permeances. Physical gelation potentially enables RTILs to be immobilized as ultra-thin selective layers on porous supports with significantly higher gas permeance than typical SILMs. It is desirable to understand and determine the mechanical properties of ultra-thin gelled-RTIL selective layers required to withstand typical flue gas process conditions. We have studied the mechanical properties of [emim][Tf₂N] gels formed using an aspartame-derived LMOG and found that they are sensitive to thermal history and processing conditions. Additionally, synthesis and preparation of supported ultra-thin gelled-RTIL membranes that are sufficiently robust to withstand realistic flue gas operating conditions is an ongoing challenge. The insights gained in this work could lead to further improvements in the design and deployment of gelled RTIL materials as high throughput gas separation composite membranes.