Interface-welded conductive skins on elastomer ionomers enable sensitive, wide-range strain sensing for pulse wave and human motion monitoring

Constructing a conductive layer on an elastomer surface decouples electrical transduction from the load-bearing function of the substrate, enabling high sensitivity and stretchability in elastomer-based strain sensors. However, interfacial integrity governs signal stability under repeated deformation. Here, an ionomer-mediated interfacial-welding strategy is developed to construct a conductive skin on a 1-(2-hydroxyethyl)imidazole-modified brominated butyl rubber ionomer (HBIIR) film. The preformed film is dip-coated in a tetrahydrofuran dispersion containing dissolved HBIIR as a binder and carbon black (CB) and whisker carbon nanotubes (WCN) as conductive fillers. The solvent swells the film surface and promotes chain interdiffusion across the coating–substrate interface. Subsequent solvent evaporation locks the interdiffused chains into an entangled interfacial network, with re-formed imidazolium–Br⁻ associations adding further interfacial cohesion. Within the skin, CB forms dense local contacts, whereas WCN provides longer-range connections between neighboring CB-rich regions. The optimized film combines a conductivity of 45.1 S m⁻ 1 with an elongation at break of 1640%. The sensor detects strains as low as 0.03%, reaches a maximum gauge factor of 14,016.92, shows response/recovery times of 154/157 ms, and maintains reproducible signals over 10,000 cycles. It records distinguishable radial pulse-wave signals at Cun, Guan, and Chi, supporting multisite pulse monitoring relevant to traditional Chinese medicine. It also enables human-motion monitoring and gesture-controlled robotic hand actuation. In addition, the sensor exhibits an antibacterial rate of 99.9% against Escherichia coli and Staphylococcus aureus . This study provides a practical route for developing sensitive, wide-range, and durable flexible strain sensors.