Janus fabric sensor with integrated moisture-wicking, wearable monitoring and thermoelectric capabilities for fire warning

Abstract

Fabric-based wearable devices have gained significant attention as next-generation flexible electronics. However, traditional fabric sensors are limited by their dense woven structures, which hinder moisture-wicking and self-powered applications. There is an urgent need to develop more portable fabric sensors that combine efficient moisture-wicking with versatile sensing capabilities. In this work, a Janus-structured fabric sensor integrating moisture-wicking (unidirectional wetting) characteristics, superior ionic thermoelectric (i-TE) properties and strain sensing capabilities was developed. The Janus fabric sensor was fabricated through a two-step sequential modification process. First, a layer of conductive polypyrrole (PPy) was synthesized directly on the fabric surface through in situ polymerization. Second, asymmetric surface modification was achieved: an i-TE gel was spray-coated onto one side of the fabric, while 3-(trimethoxysilyl)propyl methacrylate and poly(ethylene glycol) methacrylate were applied to the opposite side to create a hydrophilic surface. The i-TE gel was prepared by incorporating 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide into fluorine-modified polyurethane. The Janus fabric sensor, with its asymmetric architecture, achieved effective moisture-wicking and liquid transport against gravity within 2 s. It exhibited sensitive motion-sensing performance with a gauge factor of 9.37 while simultaneously showing outstanding thermoelectric properties, characterized by a Seebeck coefficient of 4.84 mV K⁻¹ and a power factor of 32.8 μW mK⁻². These attributes enabled the monitoring of different human activity stages in a wearable self-powered mode. More significantly, the sensor's rapid response time of 0.2 s to flame exposure enabled common household textiles to serve as fire-warning systems. It holds a great promise as a platform for next-generation smart textiles.