Wu Zhongshan University into \”ACS AMI\”: based on thermal stability, self-healing highly sensitive organic hydrogels, the temperature sensor can be stretched

In recent years, with the rapid development of wearable smart electronics industry, \”limited flexibility\” it has been difficult to meet the needs of future development, stretchability, self-healing, transparency and high sensitivity performance all the more important. In a variety of applications can be stretched system, the temperature detection is closely related to our daily lives and health care. Its ion conductive hydrogel, intrinsic stretchability, simple preparation, in response to stimuli and other advantages, has become a research hotspot stretchable electronics field. However, poor thermal stability of conventional hydrogel, dehydration and freezing stability and easy, preparation of the temperature sensor is poor, a narrow range of temperature detection, the organic hydrogel provides a new solution. In addition, the temperature-sensitive mechanism and the factors affecting ion hydrogel is not yet clear, the system to be studied. Earlier, Professor Wu Jinfu team polyacrylamide / bis carrageenan hydrogels excited ion migration in the heat conductivity lead to changes in the characteristics of the temperature sensor intrinsic preparing highly stretchable . Recently, the group by further exploring SOLVENT hydrogel Temperature Sensitive influence of its properties, ion found solvent Temperature Sensitive hydrogel has an important influence. using a solvent replacement strategy (FIG. 1), the introduction of water retention, antifreeze glycol / glycerol (EG / Gly) solvent In the conventional aqueous hydrogel converted to a solvent having a water – binary solvent system alcoholic organic hydrogels, the stability of self-repair property with good thermal, ultra-sensitive sensor temperature can be stretched further prepared.

found prolonged high temperatures (e.g., 50 , 70 ° C) treatment, conventional hydrogels had become dry, hard, and organic hydrogels thermal stability at high temperatures is significantly improved, especially after glycerol modified by organic hydrogels, the harsh under ambient conditions can be maintained for a long deformation resistance, mechanical quality and conductivity (FIG. 2). Organic hydrogels depends on the freezing point of the solvent, since the glycerol formed strong hydrogen bonds with water molecules, effective to inhibit the formation of ice crystals at a low temperature, greatly reduces the freezing point of the organic hydrogels (-120 ° C). Thanks organic hydrogel and a large number of hydrogen bonds and Reconstruction helicase carrageenan double helix, after simple heating – cooling process after completely broken gelOnly 30 minutes for efficient self-healing (FIG. 3).

temperature sensitive hydrogel mechanism: ion migration is a thermally activated process, the orientation of the ion mobility hydrogel hurdles polymer chain, as the temperature rises, on the one hand, the ion mobility is increased; on the other hand, the portion to be bound by ionic dissociation, or release, resulting in ion concentration increases, these two factors together lead to the hydrogel conductivity with temperature increases increases (FIG. 4).

By drying the solvent (water) content of the treated hydrogel regulation, we found partially dehydrated hydrogel in response to temperature significantly enhanced the sensitivity, the sensitivity increased from 2.95% / ° C to 13.1% / ° C. This may be attributed to a higher proportion of the ion in the hydrogel is partially dehydrated bound, at elevated temperatures, these ions are bound to overcome obstacles excitation heated polymer chain is free to move, on a macroscopic performance conductance significantly increased (FIG. 5).

Although the water content may be regulated by varying the thermal sensitivity of the hydrogel, but the water poor thermal stability of the gel, the organic hydrogels having both high sensitivity and thermal stability advantages. By introducing EG / Gly regulatory environment hydrogel solvent, increase the initial resistance of the organic hydrogels, and significantly improve the sensitivity of temperature detection. When the organic hydrogel is stretched to 100%, which is still higher than the heat sensitivity of 10% / ° C, the sensitivity in the case of a substantial change in bending and torsional strain is almost negligible.

This study was first discovered by solvent regulation of the hydrogel can be greatly temperature sensitive hydrogel lifting of , to expand the scope of application of hydrogel, to achieve high sensitivity and heat stable hydrogel prepared mentioned wearable electronic deviceFor a new strategy. Entitled to the results of the above \”Ultrasensitive and Stretchable Temperature Sensor Based on Thermally Stable and Self-Healing Organohydrogels\” published in the journal ACS Applied Materials & Interfaces , the first author and corresponding author for the Zhongshan University Professor Wu Jinfu. The research was funded by the National Natural Science Foundation of China, Guangdong Natural Science Foundation of China and the Guangzhou Science and Technology Program and other projects. Related literature links:.. 1 https://pubs.acs.org/doi/10.1021/acsami.0c04359#2 https://pubs.acs.org/doi/10.1021/acsami.8b03524