(507a) Characterizations of Surface Nano-Structured RO/NF Membranes: Surface Properties and Membrane Performance

Improving the performance of current RO/NF membranes requires significant reduction in membrane fouling and mineral scaling propensities. Previous strategies for mitigating membrane fouling via surface modification have relied on alteration of the membrane surface chemistry and topography by addition of a permselective polymer thin film, coated or graft polymerized, that would act both as a separation layer and a physical boundary to prevent adsorption of foulants. In the present study, a novel atmospheric pressure plasma-induced graft polymerization (APPIGP) method was developed to enable the generation of a high surface density of active surface sites on a polyamide membrane for subsequent graft polymerization using a suitable monomer. Surface structuring via graft polymerization was then carried out, using three different water soluble monomers, to form a brush layer of polymeric chains that are covalently and terminally bound to the surface. The chemical and physical features of the resulting grafted polymer films were tuned by the selection of monomer chemistry as well as the reaction conditions to achieve unique surface architectures to reduce surface fouling while achieving the desired rejection and high water permeability. The presence of grafted polymeric brush layer was elucidated by Fourier Transform Infrared (FTIR) Spectroscopy. Graft polymerization kinetics were measured with respect to the change in grafted polymer layer thickness with reaction time and monomer concentration, and the change in membrane surface energy was determined based on contact angle measurements. Furthermore, the surface nano-structured RO/NF membrane performance was evaluated by examining the membrane mineral salt scaling and biofouling propensities. Membranes fouling propensity was assessed via flux decline studies using model proteins and polysaccharides solutions. Reduction in membrane mineral scaling propensity was evaluated from both flux decline studies (using salt solutions supersaturated with respect to calcium sulfate) and using a transparent RO cell to directly evaluate the time-evolution of surface mineral crystals. The present class of membranes were of higher permeability (by up to a factor of ~2) compared to commercial RO membranes of the same level of salt rejection, but with the added benefit of significantly reduced mineral scaling propensity and comparable fouling resistant when compared with commercial low fouling RO membranes.