Novel Ionic Liquid/Poly(ether imide) Composite Membranes: Structure and Transport Properties

This study presents the development of novel composite membranes based on high-performance poly(ether imide sulfone) by incorporating 20-60 wt % of a hydrophobic protic ionic liquid, 2-butylaminoimidazolinium bis(trifluoromethylsulfonyl)imide. These composite membranes aim to address the challenge of tuning the gas separation properties in thermally and chemically stable materials. The structure-property relationships of the membranes were systematically investigated using energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, thermogravimetric analysis, and water contact angle measurements. Results revealed strong hydrogen bonding interactions between the polymer matrix and ionic liquid, leading to significant reductions in the glass transition temperature (by 84 to 218 °C) and enhanced surface hydrophilicity. The introduction of an ionic liquid up to 50% leads to a remarkable increase in the tensile strength of poly(ether imide sulfone) (by 19-42%). All membranes maintained excellent thermal stability up to 400 °C. Gas permeability testing demonstrated a nonlinear and tunable transition in transport behavior with increasing ionic liquid content. These findings offer new insights into the design of functionally graded membranes and highlight the potential of such composites for selective gas separation applications, including carbon dioxide sensing and removal from complex gas mixtures.