Ultrasensitive, Stretchable, and Fast-Response Temperature Sensors Based on Hydrogel Films for Wearable Applications

Abstract

Conductive hydrogels can be used in wearable electronics integrated with skin, but the bulk structure of existing hydrogel-based temperature sensors limits the wearing comfort, response/recovery speeds, and sensitivity. Here, stretchable and transparent temperature sensors based on a novel thin-film sandwich structure (TFSS) are designed, which display unprecedented thermal sensitivity (24.54%/°C), fast response time (0.19 s) and recovery time (0.08 s), a broad detection range (from −28 to 95.3 °C), high resolution (0.8 °C), and high stability. The thin hydrogel layer (12.15 μm) is encapsulated by two thin elastomer layers, which prevent the water evaporation and enhance the heat transfer, leading to the boosted stability and accelerated response/recovery speeds. The nondrying and antifreezing capabilities are further promoted by the hydratable lithium bromide (LiBr) incorporated in the hydrogel, enabling it to avoid dehydration in an extremely arid environment and freeze below subzero temperatures (freezing point below −120 °C). A comparative study reveals that the thermal sensitivity displayed by the TFSS sensor in capacitance mode is several times higher than that in conventional conductance/resistance mode above room temperature. Importantly, a new mechanism based on a horizontal plate capacitance model is proposed to understand the high sensitivity by considering the permittivity and geometry variations of TFSS. The thin TFSS, stretchability and transparency enable the sensor to be conformally and comfortably attached to human skin for real-time and reliable monitoring of various human motions, physical states, skin temperature, etc., without affecting the appearance.

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Porous Polydimethylsiloxane Elastomer Hybrid with Zinc Oxide Nanowire for Wearable, Wide-Range, and Low Detection Limit Capacitive Pressure Sensor

“…To meet the growing demand for wearable healthcare electronics and human-machine interfaces, nanocomposite materials that employ flexible polymers in conjunction with stimuli-sensitive nanostructures have engrossed significant attention for the consciousness of temperature [1][2][3][4][5], moisture [6,7], light [8,9], and touch [10][11][12][13]. Unlike conventional composites or a sole type of material, polymer-based nanocomposites may offer considerable enhancement in thermal, electrical, optical, chemical, or mechanical properties.…”

An Electret/Hydrogel-Based Tactile Sensor Boosted by Micro-Patterned and Electrostatic Promoting Methods with Flexibility and Wide-Temperature Tolerance

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