Hydrophilic surface modification of polyacrylonitrile based membrane: effect of low temperature radio frequency carbon dioxide plasma

Abstract

In general, polymeric membranes are hydrophobic in nature and hence are prone to fouling. Plasma treatment can impart functional groups on membrane surface making it more hydrophilic and hence fouling resistant. In plasma environment, carbon dioxide exhibits reactive properties with several exciting species and is likely to modify the membrane surface by imparting hydrophilicity. Low temperature plasma treatment using radio frequency discharge of carbon dioxide gas was employed to make polyacrylonitrile co-polymer membrane more hydrophilic. Permeability of treated membrane was increased by 2.2 times and it was retained up to 100 days. The surface morphology, structure and chemistry of the untreated and plasma-treated membranes were characterized extensively. Wettability of the surface was evaluated by contact angle measurement to show the improvement in hydrophilicity of plasma modified membrane. Effects of plasma conditions, namely, treatment time and power on membrane permeability and hydrophilicity were investigated. Hydrophilicity of modified membrane was enhanced by 22% and it was maintained up to 100 days. The effect of process variables on surface morphology of membrane was examined by scanning electron microscopy and atomic force microscopy. Surface etching due to plasma treatment was ensured by the loss of weight of the modified membranes. About 78% increase in average pore size of the treated membrane was obtained due to surface etching. The surface functionalization of unmodified and plasma modified polyacrylonitrile co-polymer membranes were investigated by X-ray photoelectron spectroscopy. Hydrophilic groups adhered to membrane surface after treatment was also identified.