Filler materials to prevent polymer intrusion into mesoporous substrates during thin film formation

The versatility and ease of synthesis of polymers have made membrane separations an attractive option for treatment of complex waters. However, most water-permeable polymers lack tolerance to corrosive environments. In our laboratory, we are developing a new class of composite membranes that incorporate water-permeable molecular sieve particles within an impermeable polymer matrix in a thin film on a porous support membrane. Together these water-selective molecular sieve particles and impermeable polymers potentially enable superior chemical resistance to harsh environments, such as extreme pH or oxidative chemicals, when compared to membranes cast using water-permeable polymers. However, using an impermeable polymer presents a unique challenge in a membrane design; if the impermeable polymer intrudes into the pores of the support material, it will block water transport through the support membrane. In this paper, we report the results of filling the pores of the support material with a liquid that is immiscible with the impermeable polymer casting solution in order to limit polymer intrusion into the support during casting. We developed a model and procedure for selecting liquid filler materials, based on a modified Washburn equation, which can be broadly applied to any solvent-polymer-support combination. Specifically, we report on the balance between the gravitational and capillary forces necessary to select a filler material that limits polymer intrusion into the support.