A sandwich-structure, low-temperature sensitive and recyclable liquid metal organic hydrogel for a wearable strain sensor

Currently, sensors based on hydrogels are less sensitive at low temperatures, and discarded sensors are prone to generate e-waste. Thus, it is challenging to design and prepare novel hydrogels with good properties for wearable sensors. Herein, we report a sandwich-structure liquid metal organic hydrogel with low-temperature sensitive, recyclable and multiple sensation properties. Liquid metal (LM)/cross-linked chitosan quaternary ammonium salt (CHACC) composite is prepared by evaporating ethanol and water co-solvent as the core layer. CHACC is used as the top and the bottom layer respectively. The optimal performance of the organic hydrogel is obtained when the volume ratio of ethanol to water is 1:3. The LM/CHACC organic hydrogel exhibits excellent stretchability (strain: 428.37%). Importantly, it has fast responsiveness, recyclability and excellent low-temperature sensitivity (GF = 8.29) at −20°C. The sensors possess stress-temperature sensation with high sensitivity. Moreover, LM as the conductive filler is recyclable under acidic conditions. We demonstrate the functionality of the LM/CHACC organic hydrogel to detect human joint movements and fine movements at low temperatures. It is anticipated to open up new sensing applications based on LM organic hydrogel-based wearable sensors.