Due to growing water shortages, reverse osmosis (RO) membranes are increasingly being considered for use in purifying alternative water sources. However, RO membranes are prone to fouling by common contaminants present in these sources, such as oil, surfactants, and particulate matter, making membrane surface modification a current area of significant interest. This study was undertaken to modify the surface of commercial polyamide RO membranes (XLE from Dow FilmTec) to make more fouling-resistant materials.

Short-chain molecules based on poly(ethylene glycol) diglycidyl ethers or fluoroalkyl oxiranes were used to form chemical bonds between their epoxide endgroups and free amines present on the polyamide RO membrane surface. Variables including treatment method (dip coating, spin coating, or stationary top surface isolation), time, temperature, and molecular weight and concentration of grafting molecule were studied for their effect on flux and rejection. The fouling resistance (i.e., flux decline) of modified and unmodified membranes was compared in crossflow filtration studies using simple model foulant solutions containing oil and/or surfactant. Grafting density (ėg/cm2) on the modified membrane surface was measured using a magnetic suspension balance. Surface properties thought to influence fouling (i.e., roughness and charge) were evaluated using atomic force microscopy (AFM, in water and air) and zeta potential analysis.