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Elucidating the impact of polymer crosslinking and fixed carrier on enhanced water transport during desalination using pervaporation membranes

Xue, Yun long, Lau, Cher Hon, Cao, Bing, Li, Pei
Journal of membrane science 2019 v.575 pp. 135-146
artificial membranes, cross-linking reagents, crosslinking, desalination, diffusivity, drinking water, pervaporation, polymers, sulfonic acid
Crosslinking is a well-established technique to enhance chemical stability of polymer membranes but at the expense of lower flux. We previously demonstrated that this trade-off between chemical stability and separation performance can be overcome through the judicious selection of a crosslinking agent, 4-sulfophthalic acid (SPTA), which also functioned as a fixed carrier site. The mechanism underpinning this breakthrough remained unknown. Through molecular dynamic simulations and a series of complementary experiments, here we reveal that higher crosslinking degree can increase local water concentration close to the sulfonic acid groups, and enhance both long-distance water-sulfonic acid-interactions and water molecule mobility. These underpinned the significant increase in water flux of crosslinked pervaporation membranes during desalination. These results show that the dependence of water diffusivity on water concentration is reduced with higher crosslinking degree. More importantly, water diffusivity at the “dry membrane region” determined the overall water transport behaviour. These findings can potentially impact on the design of pervaporation membranes for production of potable water from brackish, sea and brine water.