Manipulating membrane surface porosity via deep insight into surfactants during nonsolvent induced phase separation

Nonsolvent induced phase separation (NIPS) is a basic and classic method of preparing porous membranes. Surfactants have often been used to improve flux of porous membranes prepared by NIPS. However, not much have been reported on systematically using surfactants to control surface pore formation. Herein, the interface intermedia role of surfactants, a new understanding of the pore-making role of surfactants in NIPS, is used to tailor the surface pore of porous membrane. By controlling the known hydrophilic interaction between the hydrophilic head of surfactant and solvent, hydrophilic additive, etc., the hydrophobic interaction between hydrophobic polymer and surfactant can be varied with the hydrophobic tail of surfactant. We find that the hydrophobic interaction, represented by the compatibility between hydrophobic polymer and the hydrophobic tail of surfactant, has a vital effect on the NIPS process. As a result, this method greatly increases the surface porosity (up to 22%), optimizes the pore size distribution, and finally improves the pure water flux of polymer membranes (10-fold increase, maximally). More importantly, it has no obvious adverse effect on the mechanical strength of polymer membranes and can be extended to various polymer materials.