Dual-Charge-Switchable Membranes Using an Amphoteric Diblock Copolymer Additive

A surface charge-switchable poly(ether sulfone) (PES) membrane was developed by adding a diblock copolymer additive composed of a polystyrene (PS) hydrophobic block for anchoring in the PES matrix and a hydrophilic polyampholyte block for imparting the membrane surface with functional groups that can change between positively and negatively charged state depending on the solution pH. The polyampholyte block is a random copolymer of N,N-dimethylamino-2-ethyl methacrylate and methacrylic acid (PDMAEMA-ran-PMAAc) and, by adjusting the composition of carboxylic acid and tertiary amine groups, can display an isoelectric point at about pH 4.8. A series of PES membranes with the amphoteric diblock copolymer additive (PS-b-PDMAEMA-ran-PMAAc) were prepared using the nonsolvent induced phase inversion method; their dual-charge-switching behavior was confirmed by zeta potential, contact angle, and reversible dye adsorption and desorption measurements. Moreover, the switchable charge state of the membranes was exploited in dairy protein extraction. The results show that the additive-containing PES membrane could achieve a significantly higher productivity compared to the neat PES membrane due to enhanced antifouling and improved cleaning efficiency, underscoring the potential of using amphoteric copolymer additives in developing high-performance ultrafiltration membranes.