Mechanically ductile, ionically conductive and low-temperature tolerant hydrogel enabled by high-concentration saline towards flexible strain sensor

Abstract

Achieving a good trade-off between high mechanical performance and long-term strain sensing of hydrogel materials in cold environmental conditions remains a great challenge in the engineering fields, such as wearable electronics and human-machine interfaces. Herein, we propose a mechanically ductile, ionically conductive, anti -freezing ionic-type nanocomposite hydrogel for strain sensing under low-temperature environments. Typically, the combination use of chain-entanglement structure induced by saturated sodium chloride and nano -reinforcement produces the resultant hydrogel with the advantages of highly enhanced and balanced mechan-ical properties, reliable freezing-tolerance (-56.8 degrees C) and improved electric performance. Notably, the strain sensor based on such ionic-type nanocomposite hydrogels exhibits intriguing sensing performance, including high sensitivity (gauge factor: 6.67), fast response (approximate to 120 ms) as well as wide detection range (0-1216%). Owing to exceptional low-temperature tolerance of the hydrogels, the optimized sensor reveals a highly enhanced low -temperature adaptability and splendid sensing performance with good capacity retention (97.6% and 90.5% for electrical conductivity and gauge factor, respectively) even after storing for 30 days at -20 degrees C. Furthermore, the strain sensor can accurately detect and distinguish both large mechanical deformation and human motions under harsh environment, reflected by the unique characteristic signal with stable repeatability (e.g., a strain of 200% with 200 cycles). Clearly, the versatile multi-functionalities of high-concentration ionic nanocomposite hydrogels prepared herein could provide a new perspective for the design and fabrication of advanced all-round ionic sensor for promising applications in extremely harsh low-temperature environments.