(173b) Patterning Various Commercial Nanofiltration and Reverse Osmosis Membranes

Progressive decline in permeability due to fouling is one of the largest costs associated with membrane processes in water treatment. Innovations in membrane surface modification that limit fouling would have significant economic and societal impacts. Prior studies in this area largely have focused on chemical modifications to the membrane surface. Based on considerable literature and experience, we know that chemical modification strategies alone can be effective but not sufficient for controlling fouling. The discovery that patterning of a membrane surface can improve its fouling resistance provides an orthogonal membrane design parameter. Our hypothesis is that combining chemical modification and patterning will yield membrane surfaces that are more effective at fouling control than either method alone. This strategy is unique in its use of both chemical coating and patterning to combat fouling.

This contribution describes our method to apply a wide variety of patterns to commercial nanofiltration and reverse osmosis membranes produced using various chemistries and coatings. The goal is to better understand what factor(s) contribute to differences in patterning of thin-film nanocomposite membranes, leading to a set of heuristics that can be used by the membrane community for patterning, which is becoming a hot topic in the field. Direct patterning of 15 commercial thin-film nanocomposite membranes was done by thermal embossing using nano- and micropatterned stamps. Patterning studies began by embossing all membranes at one set of fixed conditions followed by AFM characterization. These initial studies uncovered the strong membrane chemistry dependence on pattern replication that sparked a more comprehensive study using controlled conditions of force and time with varying temperatures. AFM, SEM, and laser scanning microscopy (LEXT) were used to determine the extents of patterning. AFM and LEXT were used to determine the local strain as a function of embossing conditions. Membrane performance was evaluated by measuring flux and salt rejection using a magnesium sulfate solution. Flux and salt rejection properties were compared to local strain values and Young’s Modulus values of the patterned membranes to establish correlations.