Entropy-Engineered Fiber-Shaped Liquid Crystal Elastomer Based Thermocell Integrated into 3D-Knitted Wristbands for Sensing Application

Abstract

Thermocell (TEC), as economical, simple, and stable-output ionic thermoelectric (i-TE) systems, provides a reliable solution for the effective utilization of low-grade heat and direct conversion to continuous electricity. However, prevalent issues in TEC, such as electrolyte leakage, low tensile toughness, and limitations in the fabrication of series/parallel planar devices, have restricted its practical applicability. Herein, a quasi-solid, fiber-shaped 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF₄)-liquid crystal elastomer (E-LCE) based TEC is obtained by impregnation with I₂/KI/EMIM BF₄ solution, leveraging the chaotropic effect of BF₄⁻ and the interaction of EMIM⁺-I₃⁻ to expand the entropy and potential differences between the hot and cold electrodes, achieving a thermopower of −1.2 mV K⁻¹. Furthermore, combining traditional weaving techniques and three-dimensional structural embedding design, an E-LCE-based TEC wristband is woven by integrating the TEC into an LCE ribbed textile, achieving accurate monitoring of the wearer’s body temperature, broadening the application scenarios of TEC and paving the way for its commercial applications in wearable devices and biomonitoring fields.

Graphical Abstract

This work uses Liquid Crystal Elastomer (LCE) as the substrate and employs I₂/KI as the redox couple. The chaotropic effect of EMIM BF₄ not only increases the entropy difference of the system but also serves as a supporting electrolyte to enlarge the potential difference, thereby synergistically improving the thermoelectric properties of the LCE based TEC. Finally, leveraging the mechanical advantages of the LCE material together with the stable and rapid voltage response of the LCE-based TEC, an LCE-based i-TE wristband was fabricated and applied for human body temperature monitoring.

Keywords

Thermocell / Liquid crystal elastomer / Entropy-engineered / 3D-knitted wristbands

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Funding

the National Natural Science Foundation of China(U23A20685)

the National Natural Science Foundation of China (U24A2061)

the Innovation Program of Shanghai Municipal Education Commissio(202101070003E00110)

Shanghai Committee of Science and Technology (23520710300)

Shanghai Committee of Science and Technology(24YF2700400)

AI-Enhanced Research Program of Shanghai Municipal Education Commission(SMEC-AI-DHUY-04)

RIGHTS & PERMISSIONS

Donghua University, Shanghai, China