(718c) Surface Nano-Structuring of Polysulfone UF Membrane Surfaces

Membrane fouling remains as one of the major operational difficulties in both UF and RO membrane technologies. Various approaches have been proposed over the last four decades to modify membrane surface chemistry and topography in order to increase membrane fouling resistance. In the present work, surface nano-structuring via atmospheric pressure plasma-induced graft polymerization (APPIGP) has been developed to tailor-structure both polysulfone and polyamide UF and RO membrane surfaces, respectively, so as to increase surface hydrophilicity and thus also increase fouling resistance via the presence of a high density layer of terminally-anchored hydrophilic polymer chains. These nano-structured surfaces are created by generating high density of surface active sites on the base membrane surface, from which vinyl monomers are graft polymerized to create dense, terminally and covalently-bonded polymer brush layers. The above APPIGP approach was utilized to nano-structure polysulfone (PSf) membrane surfaces via graft polymerization of acrylic acid and 2-hydroxyethyl methacrylate monomers. The achieved level of surface hydrophilicity was evaluated with respect to surface activation via plasma treatment (i.e., reactive plasma gas species, radio frequency (RF) power, and plasma exposure time) and graft polymerization (i.e., initial monomer concentration, reaction temperature, and grafting time) conditions. The resulting modified polysulfone surface properties (chemistry and topography of polymer brush layers) were characterized by atomic force microscopy (AFM), contact angle measurement, and X-ray photoelectron spectroscopy (XPS). The results showed that significant reduction of surface wettability was achieved upon graft polymerization. Moreover, surface hydrophilicity and roughness of the modified polysulfone surface can tuned by varying plasma and grafting conditions, indicating that the APPIGP methodology could be beneficial for surface modification of commercial polysulfone UF membranes for improving the surface hydrophilicity and hence fouling mitigation.