Enhancing air-dehumidification performance of polyimide membranes by generating hydrophilic Poly(amic acid) domains using partial hydrolysis

Membrane-based air-dehumidification has been considered as one of the most promising technologies for the next-generation heating, ventilation, and air-conditioning (HVAC) systems. Though attractive, polymeric membranes suffer from limitation between their H₂O/N₂ separation performance (i.e., H₂O/N₂ separation factor and H₂O permeability) and their mechanical stability. Herein, we propose a facile and effective strategy, controlled partial hydrolysis, to improve the H₂O/N₂ separation performance of polyimide (PI) membranes while maintaining their mechanical stability. Controlled hydrolysis turned the PI membranes partially into poly (amic acid) (PAA)/PI membranes, exhibiting an asymmetric configuration with the inner layers more hydrolyzed. Interestingly, the hydrolysis in a highly concentrated NaOH solution led to formation of localized domains that were hydrolyzed (i.e., PAA domains). The localized hydrolysis of mechanically stable PI membranes led to formation of hydrophilic PAA channels embedded in the PI, thereby enhancing H₂O/N₂ separation performance (i.e., H₂O permeability from ~6400 Barrer to ~11,000 Barrer and H₂O/N₂ separation factor from ~190 to ~ 320) while preserving the mechanical strength of the membranes.