Vacuum UV (VUV) Photo-Oxidation of Polyethersulfone (PES)

International need for water quality is placing a high demand on separation technology to develop advanced oxidative processes for polyethersulfone (PES) membranes to help improve water purification. Therefore, VUV photo-oxidation with a low pressure Ar plasma was studied to improve the hydrophilicity of PES by flowing oxygen over the surface during treatment. X-ray photoelectron spectroscopy (XPS) detected a decrease in the C at% (4.4 ± 1.7 at%), increase in O at% (3.7 ± 1.0 at%), and a constant S at% (5.4 ± 0.2 at%). Curve fitting of the XPS spectra showed a decrease in sp2 C-C aromatic group bonding, and an increase in C-O, C-S, O=C-OH, sulphonate (-SO3) and sulphate (-SO4) functional groups with treatment time. The water contact angle decreased from 71.9° for untreated PES down to a saturation level of 41.9° with treatment. Since scanning electron microscopy (SEM) showed no major changes in surface roughness, the increase in hydrophilicity was mainly due to oxidation of the surface. Washing the VUV photo-oxidized PES samples with water or ethanol increased the water contact angle saturation level up to 66° indicating the formation of a weak boundary layer.