Latex particle rejections from virgin and mixed charged surface polycarbonate track etched membranes

In this study, the impact of membrane surface characteristics on particle rejections was experimentally examined for virgin and surface modified polycarbonate track etched microporous membranes with different pore sizes. The membrane surface was modified by covalently binding tetraethylpentamine, resulting in changes in measured zeta potential. The zeta potential of the modified membranes was pH sensitive, indicating these membranes had mixed surface charges, with the tetraethylpentamine binding to only a fraction of the carboxylic acid groups on the original polycarbonate surface. There was no observable change in pore size with the surface modification. Rejections of 0.71 μm diameter negatively charged spherical red fluorescent latex particles were measured under conditions where the virgin membranes carry a strong negative charge and the surface modified membranes carry a net zero charge. Observed particle rejections from both types of membranes were two to three times larger than predictions based on steric particle-membrane interactions. These results are interpreted by considering particle adsorption to the membrane surface which is greater for the modified membranes than for the virgin membranes. This work demonstrates that mixed charged membrane surfaces show enhanced fouling, in contrast to previous studies which have shown reduced fouling for membranes with zwitterionic surfaces.