Effect of solvent power on the rheological properties,morphology,porosity and separation performance of PSf flat sheet membranes

This study shows that the lacy structure could be efficiently formed and retained in polysulfone (PSf) membrane morphology by 2-pyrrolidone (2P) as a poor solvent instead of N-methyl pyrrolidone (NMP) during the non-solvent induced phase separation process (NIPS). With 2P, the PSf membrane involved a porous skin layer, lacy structure and fewer macrovoids, while with NMP a dense skin layer, finger-like macrovoids and cellular structure were dominant. The use of 2P increased the viscoelasticity of the polymer solution. The enhanced viscoelasticity of the PSf/2P solution slowed down the growth rate of demixed domains during the liquid-liquid demixing process due to the formation of hydrogen bonding between PSf chains and 2P molecules in the solution. The gelation of polymer-rich phase inhibited the coarsening of the phase-separated domains, and consequently, the lacy structure formed and locked in the nascent PSf membrane. The lacy structure formation, as well as the size and shape of the macrovoids in the PSf membranes, were changed by the utilization of 2P in the system. Also, the performance results showed that the flux is enhanced and salt rejection is declined with 2P in the dope solution.