(593a) Constant Flux Crossflow Filtration Evaluation of Bioinspired Fouling-Resistant Membranes

Polydopamine, formed by the spontaneous polymerization of dopamine in buffered, aqueous solution, has recently found use as a hydrophilic surface modification agent.  Polydopamine is a catecholamine polymer inspired by the adhesive proteins secreted by many sessile marine organisms, and has been found to form a robust coating on a wide variety of polymeric membranes.  In addition to hydrophilizing the surface, polydopamine can also be used as a surface primer for the conjugation of other molecules, such as poly(ethylene glycol).  The surfaces of polysulfone ultrafiltration membranes were modified with polydopamine and polydopamine-g-poly(ethylene glycol) hydrophilic coatings.  Unmodified and modified membranes were challenged with a soybean oil emulsion feed at six different permeate fluxes in constant flux crossflow filtration fouling studies.  The threshold flux was determined for each membrane.  Above the threshold flux, modified membranes generally exhibited lower transmembrane pressures than unmodified membranes.  However, below the threshold flux, modified membranes had higher transmembrane pressures than unmodified membranes, likely due to an increase in mass transfer resistance resulting from the surface modification.  If the membranes are to be operated below the threshold flux to achieve sustainable operation, one might conclude that these surface modifications did not improve the overall performance of the membranes during fouling, since the resistance to mass transfer of the modified membranes was not lower than that of the unmodified membrane.  However, the surface-modified membranes had a lower pure water permeance, and, therefore, higher initial resistance, than the unmodified membrane.  To account for this difference, polydopamine-g-poly(ethylene glycol) modified membranes were compared to membranes with a thicker polydopamine coating and to an unmodified membrane with a smaller pore size than that used in the surface modification studies; in this way, all three membranes had similar initial resistances.  In this case, the unmodified membrane exhibited a much higher transmembrane pressure during fouling than the modified membranes, so when membranes are compared at the same initial resistance, the surface modifications improved fouling resistance.  Therefore, a potential strategy to achieve fouling resistance in a membrane of a desired flux and rejection is to modify the surface of a more permeable (and perhaps lower rejection) membrane, thereby making the resulting modified membrane fouling resistant but leaving it with the desired flux and rejection characteristics.