Self-assembled nanostructured membranes with an imidazolium-sulfonate betaine group: Ionic columnar liquid crystals on water treatment and CO2 gas separation properties

Abstract

Ionic liquid crystals have various potential applications enabling selective and effective transportation. Herein, we report the development of a separation membrane prepared by fixing the liquid-crystalline (LC) columnar (Col) nanostructures through in situ polymerization of the film states formed by imidazolium-sulfobetaine ionic liquid crystals. We compared the properties of the nanostructured betaine liquid crystals with those of analogous Col structures containing mono-ionic groups such as imidazolium and trialkyl ammonium moieties. The betaine LC compounds formed more thermally stable LC phases than the mono-ionic LC compounds having analogous structures. For salt permeation in water treatment, the betaine LC membrane exhibited ion selectivity, that was different from those of the mono-ionic LC membranes. During the virus filtration, the water flux of the betaine membrane was the highest among other analogous nanostructured Col membranes. For gas separation, these Col LC membranes showed selective CO₂ permeation properties and exhibited the αCO₂/N₂ selectivity of about 30 under highly humidified conditions.