Facile fabrication of stretchable, anti-freezing, and stable organohydrogels for strain sensing at subzero temperatures†

Abstract

Conductive hydrogel-based soft devices are gaining increasing attention. Still, their dependence on water makes them susceptible to freezing and drying, which affects their long-term stability and durability and limits their applications under subzero temperatures. Developing hydrogels that combine exceptional strength, high strain sensitivity, anti-freezing properties, synchronous sensing, durability, and actuating capabilities remains a significant challenge. To overcome these issues, a universal solvent replacement strategy (USRS) was adopted to fabricate anti-freezing and anti-drying organohydrogels with ultra stretchability and high strain sensitivity in a wide temperature range. Ethylene glycol (Eg) and glycerol (Gl) were used as secondary solvents to replace water (primary solvent) from the hydrogel network. Due to the strong hydrogen bonding capabilities of Eg and Gl with water and the hydrogel network, the organohydrogels formed show resistance to freezing and drying. This allows the organohydrogels to maintain conductivity, sensitivity, stretchability, and durability under subzero temperatures. The developed organohydrogels display remarkable stretchability (850%), good electrical conductivity (0.45 S m⁻¹), exceptional anti-freezing performance below −90 °C and very high sensitivity (GF = 10.14). Additionally, the strain sensor demonstrates a notably wide strain range (1–600%) checked within the temperature range of −15 °C to 25 °C. It also effectively monitors various human movements with differing strain levels, maintaining good stability and repeatability from −15 to 25 °C. It is also believed that this strain sensor can work efficiently above and below the mentioned temperature range. This study introduced a straightforward approach to developing conductive organohydrogels with outstanding anti-freezing and mechanical properties, demonstrating significant potential for use in wearable strain sensors and soft robotics.