Anion-Influenced Hydration and Layering Vastly Modulate Polyzwitterionic Brush Responses

This study investigates the influence of different anions on the hydration states and conformational changes of poly(sulfobetaine methacrylate) (PSBMA) brushes, unraveling their intricate role in modulating tribomechanical properties and antifouling performance. Through bimodal atomic force microscopy (AFM), we reveal that anion identity affects the layered structure thicknesses of PSBMA brushes in accordance with the Hofmeister series. Enhanced screening of dipole–dipole interactions and increased hydration were observed with higher concentrations of more chaotropic counterions, showcasing the anti-polyelectrolyte effect (APE), a phenomenon that was not observed in highly kosmotropic sulfate anions. Infrared spectroscopy highlighted the impact of anions on the incorporation of strongly H-bonded water clusters within the PSBMA chains. Our findings underscore the complex interplay of interfacial interactions (chain dipole–dipole, ion-chain dipole, ion–water, and water-chain dipole), leading to variations in tribomechanical behavior and antifouling performance of PSBMA brushes. Pearson correlational analysis with anion descriptors further elucidated these relationships, offering insights for tailored material design in engineering applications, thus advancing materials science and biotechnology.