Journal of Membrane Science, 2019, vol 582pp. 391-401
Evaporation is significantly important for the preparation of isoporous membranes from self-assembly and non-solvent induced phase separation (SNIPS). Unfortunately, the time of solvent evaporation that retains isoporous structures is usually rather short, which causes many challenges to fabricate membranes with repeatable and controllable isoporous structures. In the current work, we used organic acids to tailor and enlarge the time window that led to isoporous structures, and their effects on membrane formation were investigated. It was found that binary and ternary organic acids all worked effectively and were able to extend the time window that produced isopores to longer than 200 s. In previous publications, this time duration was commonly in the range from several to tens of seconds. The nuclear magnetic resonance (NMR) determination implied that molecular cross-linking between acids and copolymers was existed in solution, and results from small angle X-ray scattering (SAXS) analysis demonstrated that the microphase separation of the block copolymer in casting solution was enhanced by the selected acids. The results proved that binary and ternary acids added to casting solution had not only enhanced the microphase separation but also stabilized the phase separated domains, which was ascribed as the reason for the extension of the time window. The effectiveness of organic acids on broadening the time window was also found for casting solutions of different concentrations and solvent compositions. Besides the role on stabilization of isoporous structure, the flux of isoporous membrane was also greatly increased by the organic acids.