Phase-Programmed Ionogels Enabling Decoupled Strain–Temperature Sensing with Negligible Hysteresis and High Resolution for Intelligent Fitness Monitoring

Simultaneous sensing of mechanical and thermal stimuli in soft ionotronics remains a challenge because ionic conductors couple thermal activation and mechanical deformation through shared transport pathways. Here, we report an ionogel platform achieving signal decoupling through a materials-to-architecture modulus programming. Polymerizing poly(acrylic acid) (PAA) inside hydrophilic-hydrophobic binary ionic liquids triggers solubility-driven phase separation, modulating the modulus from ∼10 kPa to ∼10 MPa. Architecturally, we engineered an alternating Hard-Soft-Hard ionogel array where interpenetrating PAA networks polymerize across the units to form chemically bonded interfaces without secondary bonding. The PAA-rich hard domains act as strain-invariant thermistors (local strain <0.04%), delivering 0.01 °C temperature resolution and negligible hysteresis (1.64%). Simultaneously, the soft domains function as linear strain and directional sensors. Integrating this platform with AI algorithms enables smart monitoring during fitness routines. Leveraging phase separation for functional partitioning offers a novel perspective on simplifying multimodal sensor design.