Fine-tuning of the surface porosity of micropatterned polyethersulfone membranes prepared by phase separation micromolding

Phase separation micromolding (PSμM) is an effective technique for fabricating porous membranes with micropatterned structures. However, reports on procedures to control the size and number of open pores on the patterned surface are scarce, which often limits the use of the surface-patterned membranes. This work presents a systematic study on tailoring open pores on the patterned surface of polyethersulfone (PES) membranes prepared by the PSμM procedure. The composition of the solvent and the concentration of PES in the casting solution were optimized to tune the size and number of pores on the membrane surfaces formed on a flat substrate during the nonsolvent-induced phase separation (NIPS) process. The surface porosity changed significantly and macrovoids appeared when the flat substrate was replaced by a micropatterned substrate. The vapor-induced phase separation process was applied prior to the NIPS process to prevent the formation of macrovoids. The composition of the casting solution was tuned again to prepare micropatterned porous PES membranes with open pores on the patterned surface. We observed that the size and number of pores were different depending on the pore locations on the patterned surface, which was caused by different solvent/nonsolvent demixing dynamics resulting from the physical discontinuity of micro-patterned membranes.