(743d) Effect of Membrane Surface Chemistry on Grafting Density and Molecular Weight Cutoff
Water membranes usually suffer from fouling issue which can lead to a dramatic decrease in membrane productivity. This phenomenon can be mitigated through hydrophilizing the membrane surface. Zwitterions (ZWs) and poly (ethylene glycols) (PEGs) have been widely used to make antifouling membranes by enhancing the surface hydrophilicty. A facile method to graft the antifouling ZWs and PEGs onto the membrane surface is co-depositing with dopamine, which can easily be polymerized to an adhesive agent, polydopamine (PDA). PDA can enhance the membrane surface hydrophilicity, and, simultaneously, bind ZWs or PEGs onto the surface. However, increasing the content of grafted ZWs or PEGs into the coating layer still remains a challenging issue which needs to be studied. PDA can react with either acrylate or amine functional groups through Michael Addition. In this work, two series of ZWs and PEGs (acrylate-terminated and amine-terminated compounds) are co-deposited with dopamine onto the silicon wafers and ultrafiltration (UF) membranes. Acrylate-terminated compounds include sulfobetaine methacrylate or SBMA and PEG-diacrylate or PEGDA and amine-terminated compounds include a sulfobetaine ZW, functionalized with the primary amine, or SB-amine and PEG-diamine. To achieve the highest grafting density of ZWs or PEGs, co-deposition times and concentrations of ZWs or PEGs were varied, under a constant dopamine concentration (1 g/L). Results obtained from thickness measurements, conducted on the silicon wafers, exhibited significant contents of grafted ZWs or PEGs into the coating layers. Tuning the grafting conditions led to enhance the SBMA or PEGDA contents up to 38% and 64%, respectively. In the case of PEG-diamine, even when co-deposited under a lower concentration, compared with that of PEGDA, its content reached about 72% in the coating layer. Such this behavior demonstrates the PDA-amine interactions can graft a higher content of polymers onto the surface, than that of the PDA-acrylate interactions, under the same co-deposition time and dopamine concentration. The proposed surface modification was also applied to a polysulfone UF membrane (PSf) with the molecular weight cutoff (MWCO) of 25 kDa. The modified membranes with dopamine and ZWs or PEGs (for both cases of acrylate- and amine-terminated compounds) indicated lower water contact angles, compared with those of uncoated ones, suggesting increasing the membrane surface hydrophilicity. We will also systematically compare the effect of the surface chemistry on the MWCO and water permeance of the PSf membarne, aiming to derive the structure/property relationship.