Robust and Wide-Range Friction Regulation via Interfacial Bridging-Promoted Hydration Switching in Phase-Separated Gels

Interfacial friction strongly influences materials performance, but achieving controllable friction with both high robustness and wide-range tunability remains difficult. In conventional friction regulation systems based on phase separations, rigid and incompatible hydrophilic–hydrophobic interfaces often cause interfacial cracking and poor stability. Here, inspired by the toughening mechanism of cartilage, we introduce amphiphilic bridging segments between hydrophilic and hydrophobic phases to construct an interfacial bridging nanophase-separated gel (IBNSGel) for robust friction control. This design transforms the fragile phase interface into a tough bridging interphase, suppresses aggregation, promotes uniform nanophase separation, and enhances interfacial stability during hydration-induced phase separation. Owing to this bridging effect, IBNSGel exhibits synergistic surface-bulk friction switching upon hydration: the surface forms a stable hydration layer for excellent lubrication, while the bulk hardens with higher modulus and lower damping, reducing conformal contact dissipation. As a result, this gel achieves stable, reversible, and wide-range coefficient of friction (CoF) switching during hydration–dehydration, with switching ratios of 150 at the macroscale and 330 at the microscale. Based on its excellent multimedium stability and biocompatibility, this friction control material demonstrates great application potential in smart medical devices, soft robots, and interface intelligent transportation systems.