Polysulfone surface nano-structured with tethered polyacrylic acid

Tethered poly(acrylic acid) (PAA) chains, synthesized onto polysulfone (PSf) surfaces, were characterized with respect to surface topography and chain characteristics via AFM force spectroscopy. The tethered PAA chains were synthesized by surface activation with an impinging atmospheric pressure plasma stream (He, He/O-2 and He/H-2), followed by free-radical acrylic acid graft polymerization. The number average molecular weight of the tethered PAA chains was estimated to be of in the range of similar to 13,000-35,000 with chain-chain separation of 1.5-2.4 nm. Deionized and high salinity water contact angles for the PAA-PSf surfaces were in the range of similar to 29-38 degrees, indicating hydrophilic surfaces, relative to 80 degrees contact angle for the native hydrophobic PSf surface. In DI water the tethered PAA chains had significantly greater chain extension than in a high salinity aqueous environment Ultrafiltration fouling stress tests with alginic acid in a high salinity water and post cleaning with non-saline water demonstrated permeability restoration of up to 90-100% for a PAA-PSf membrane relative to 50-70% for the native PSf membrane. The present study suggests the merit of exploring and optimizing surface modification of membranes for saline water filtration to reduce irreversible fouling and improve cleaning effectiveness using non-saline water.