Colloidal adhesion to hydrophilic membrane surfaces

Abstract

Colloidal adhesion to membrane surfaces is an important parameter in determining membrane fouling propensity and in optimizing membrane cleaning strategies. It has previously been demonstrated that acid–base interactions can significantly affect colloid–membrane interaction as a colloid approaches a membrane surface, however, the effect of acid–base interactions on adhesion has received less attention. In this investigation, the approach and adhesion of a silica and polystyrene colloid was measured on three commercially available hydrophilic water treatment membranes using an atomic force microscope and the colloid probe technique. It was found that the hydrophobic polystyrene colloid adhered more weakly to each membrane compared to the hydrophilic silica colloid. These results could not be resolved through classic DLVO analysis alone and were in direct contrast to the expected interaction based on the strong hydrophobic character of the polystyrene colloid. However, the results could be explained by considering the magnitude of the surface’s electron-acceptor ( γ +) and electron-donor ( γ −) components. It is hypothesized that through hydrogen bonding with surface γ + and γ − groups, structured water layers exist to varying extents at the surfaces of the silica colloid and the hydrophilic membranes, and that their removal results in the formation of strong adhesive bonds between reciprocal γ + and γ − groups. Furthermore, even when surface roughness is substantial, γ + and γ − groups appear to play some role in determining the magnitude of the measured adhesion. The lack of such groups on the polystyrene colloid, and thus the lack of hydrogen bonding capacity, was responsible for its weaker adhesion with the membranes.