Ionic strength-responsive poly(sulfobetaine methacrylate) microgels for fouling removal during ultrafiltration

Zwitterionic materials have received a lot of interest in the field of membrane science and water treatment due to their excellent fouling resistance, super-hydrophilicity, and ionic strength response. However, they have typically been utilized for surface functionalization. In this study, we report the synthesis of zwitterionic poly(sulfobetaine methacrylate), p(SBMA), microgels, and demonstrate the effect of their ionic-strength responsive behavior on the extent and reversibility of fouling on ultrafiltration membranes using Bovine Serum Albumin (BSA) and Baker's yeast as model foulants. The microgels synthesized using inverse emulsion free radical polymerization showed ionic strength response with increasing hydrodynamic diameter from 208 ± 4 nm to 316 ± 7 nm with increasing NaCl concentration from 0 to 0.5 M. The size change upon changing ionic strength was utilized by two approaches: co-depositing microgels with the foulants, and pre-depositing microgels on the membrane. When the microgels were co-deposited with the foulants, there was a small improvement in fouling reversibility while when the microgels were first deposited on the membrane by filtering them through, there formed a stable, continuous layer of p(SBMA) on the surface which clearly increased the fouling reversibility