Preparation of рН-Responsive PET TeMs by Controlled Graft Block Copolymerisation of Styrene and Methacrylic Acid for the Separation of Water-Oil Emulsions

To develop membranes capable of efficient and switchable separation of emulsions under variable pH conditions, pH-responsive surfaces were engineered by modifying poly(ethylene terephthalate) track-etched membranes (PET TeMs) via a two-step UV-initiated RAFT graft polymerization. Initially, polystyrene (PS) was grafted to render the surface hydrophobic, followed by the grafting of poly(methacrylic acid) (PMAA) to introduce pH-responsive carboxyl groups. Optimized conditions (117 mM MAA, RAFT:initiator 1:10, 60 min UV exposure at 10 cm) resulted in PET TeMs-g-PS-g-PMAA surfaces exhibiting tunable wettability, with contact angles shifting from 90° at pH 2 to 65° at pH 9. Successful grafting was confirmed by FTIR, AFM, SEM, TGA, and TB dye sorption. The membranes showed high separation efficiency (up to 99%) for both direct and reverse emulsions. In direct emulsions, stable flux values (70 to 60 L m-2 h-1 for cetane-in-water and 195 to 120 L m-2 h-1 for o-xylene-in-water) were maintained over five cycles at 900 mbar, indicating good antifouling behavior. Reverse emulsions exhibited initially higher flux, but stronger fouling; however, flux recovery reached 91% after cleaning. These findings demonstrate the potential of PET TeMs-g-PS-g-PMAA as switchable, pH-responsive membranes for robust emulsion separation.