Ionic Responsiveness of pSBMA Zwitterionic Polymer Brushes: An Atomic Force Microscope Investigation into Interfacial Mechanistic Insights

Zwitterionic polymer brushes, containing both anionic and cationic groups, exhibit a characteristic antipolyelectrolyte effect-manifested as chain extension upon increasing salt concentration-which reinforces a stable hydration layer that effectively resists protein adsorption and microbial adhesion. Ionic stimuli further modulate brush stiffness, thickness, and conformational flexibility, thereby tuning interfacial properties such as lubrication, adhesion, and selective permeability. In this study, atomic force microscopy was used to quantify the mechanical response of poly(sulfobetaine methacrylate) (pSBMA) brushes under varying concentrations of mono-, di-, and trivalent cations. Results show that at low ion concentrations, both brush stiffness and friction coefficient decrease, while at high concentrations, these properties increase-trends that are more pronounced with increasing cation valency. This discovery experimentally reveals the intrinsic mechanism of ion-brush interactions in the polymer brushes of the pSBMA system, laying a theoretical foundation for designing zwitterionic coatings with tunable surface properties.