Studying the effect of feed water characteristics on the hydrophobicity of cellulose acetate ultrafiltraion membranes and its correlation to membrane morphology: A chemical force microscopy approach

The complexity and variability of solute chemistry which forms the conditioning layer with the membrane surface (i.e., instantaneous fouling) makes it hard to distinguish between abiotic and biotic fouling behaviors. Moreover, the role of membrane chemical heterogeneities and morphology in biofouling and their effect on solute chemistry has received little attention. In this research, the effect of two feed water characteristics (i.e., conductivity and pH) on the membrane-solute interaction forces (i.e., hydrophobic attraction), and its correlation to membrane morphology was assessed. The surface hydrophobicity, and in turn, hydrophobic attraction forces of cellulose acetate ultrafiltration (CAUF, MWCO 20,000 Dalton) membranes were assessed using chemical force microscopy (CFM) to measure surface adhesion. CFM was applied in lateral mode to correlate the difference in the adhesion forces, on the membrane surface, with its topography. Spatially resolved friction images, from CFM scans in lateral mode, were generated on membranes using DI and tap water. Adhesion force analysis showed that as feed water conductivity increased, the range of the adhesion force increased. In addition, friction forces increased when adhesion forces increased on the membrane surface.