Effect of air gap induction on the morphological microstructure of polyether sulfone hollow fiber membrane

Abstract Polyether sulfone hollow fiber membrane was prepared via nonsolvent‐induced phase separation process using dimethylacetamide (DMAc) as a solvent, Polyvinylpyrrolidone (PVP‐K30) and water as additives. The mechanism of air gap environment in the membrane structure formation was studied. The scanning electron microscope microstructure morphology revealed that the air gap environment induced the microstructure formation of membranes. The low humidity air gap environment was not conducive to the surface pore formation and hard to obtain surface pores until lowering the dope solution temperature. The high humidity can easily induce the formation of large out surface pore structure along with the decreases of the surface pore uniformity. As air gap humidity and distance increased, the membrane cross section structure near the outer surface tends to be looser and that near the inner surface became denser, while the proportion of finger‐like pores in the cross section initially increased and stabilized. At 100 RH, the average outer surface pore size increased from 0.192 μm at an air gap distance of 20 cm to 0.351 μm at 50 cm, the corresponding pore density decreased from 2.66 to 1.13 pores/μm 2 , and the percentage of the inner skin layer thickness increased from 3.26% to 7.69%.