Thermochromic-Based Bimodal Sensor for Strain-Insensitive Temperature Sensing and Synchronous Strain Sensing

High-sensitivity flexible sensors have broad applications, but their cross-sensitivity to temperature variations and deformations often results in unwanted signal interference, significantly hindering their real-world implementation. Herein, we present a unique bimodal sensor that, for the first time, achieves thermochromic-based strain-insensitive temperature sensing while also displaying synchronous strain sensing without signal interference. This bimodal sensor is based on a dual-network hydrogel, combining a poly(ionic liquid) (PIL) with UCST behavior and a neutral polymer with LCST behavior. By adjusting the LCST/UCST network ratio, polymer concentration, and hydrophilicity of the LCST network, these sensors demonstrate a broad range of operating temperatures (~65 ℃), ultra-high temperature detection sensitivity (10.13 %/℃), and a favorable gauge factor within the low strain region. Meanwhile, we investigated the microscopic mechanism of the bimodal sensor using SAXS and 2Dcos IR analysis, which revealed the strain-insensitive change in transmittance is due to the transition between the ellipsoidal and core-shell phase domains in the double-network (DN) hydrogel, related to subtle changes in the interactions between different polymer chain segments and H2O. This work not only expands design ideas to eliminate signal interference between temperature variations and deformations but also provides a highly sensitive sensing unit for advanced smart wearable electronics.

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