Salt-Percolated, Anti-Drying, Anti-Freezing and Transparent Hydrogels for Stretchable Temperature and Strain Sensor

This paper presents a facile and versatile salt-percolated method to synthesize anti-drying and antifreezing hydrogels for wide-range temperature detection and tiny strain monitoring. Lithium bromide (LiBr) is verified as the most effective drying and freezing inhibitor for hydrogels among various salts. The hydrogels with 50wt% LiBr percolation retain high stretchability (400% and 625% strain) even upon exposure to ambient for one year or at −78.5 °C. The density functional theory (DFT) simulations reveal that the high binding energy between H2O and Li⁺/Br is responsible for the excellent drying and freezing tolerances of salt-percolated hydrogel. The salt percolation method endows hydrogel with improved sensing performance. The thermal sensitivity of the temperature sensor is promoted from 1.89%/°C to 2.54%/°C and the response time is reduced from 202.6 to 53.6 s. The high resolution of strain sensor (0.1% strain) enables the salt-percolated hydrogel to detect various kinds of physiological signals, which exhibits great promise for wearable applications.