Janus Hydrophobic Structural Gel with Asymmetric Adhesion in Air/Underwater for Reliable Mechanosensing

Abstract Reliable interfacial bonding is an essential guarantee that flexible electronics can output realistic signals, especially for underwater scenes. However, conventional self‐adhesive materials usually suffer from underwater adhesion failure, conflict between adhesion and cohesion, as well as adverse effects of isotropous adhesion and residue, greatly limiting their applications in flexible electronics. Herein, a Janus hydrophobic structural gel (HSG) with asymmetric adhesion is fabricated by a “grafting one twig on another” approach (in situ constructing a hydrophobic anti‐adhesive gel on the top of a hydrophobic self‐adhesive gel). The hydrophobic adhesion layer with long C18 aliphatic chains achieves a reliable underwater bonding (interfacial toughness exceeds 80 J m −2 ) with the assistance of high mobility of polymer chains, multiple interfacial interactions, and effective removal of interfacial liquid. The hydrophobic anti‐adhesion layer containing poly(ionic liquid) is more robust due to electrostatic and ion‐dipole interactions, ensuring the mechanical strength of the integral HSG. Such asymmetric heterostructure avoids common nonessential adhesion and residue, facilitating operation. The intrinsic hydrophobicity of HSG also prevents water erosion, achieving reliable underwater adhesion and sensing. As a result, the assembled sensor based on HSG can stably monitor human motions and wirelessly transmit underwater information, exhibiting an enormous potential in wearable electronics.