Antifreezing and Temperature-Responsive Ionic Hydrogels with Applications in Encryption and Sensor Technologies

The use of thermoresponsive hydrogels for applications such as sensors, thermal gates, smart windows, actuators, and molecular devices has increased in popularity in the past decade. However, existing thermoresponsive biobased hydrogel sensors face challenges in rapidly responding to ambient temperature changes and retaining flexibility at subzero temperatures. To overcome these limitations, a novel hydrogel composed of dextrin, glycerol, and the ionic liquid monomer tetrabutylphosphonium styrenesulfonate (PSS) was developed and utilized as a smart sensor material for the first time. The thermoresponsive characteristics of PSS endow the hydrogel with remarkable thermoresponsiveness, which is a lower critical solution temperature (LCST)-type phase transition. In addition, the hydrogel can be used as a thermally responsive material over a broad temperature range of 20-60 °C. We used glycerol and glycidyl methacrylate dextrin (Dex-GMA) monomers with a multihydrogen bond structure to construct a Dex-GMA-PSS conductive hydrogel with antifreeze properties even at -20 °C. Hence, the hydrogels formulated in this study exhibit promising potential for several applications, including flexible wearable devices, skin-like sensors, advanced anticounterfeiting, and encryption technologies across a broad temperature range.