Highly flexible phase-change film with solar thermal storage and sensitive motion detection for wearable thermal management

The utilisation of phase-change materials (PCMs) for the thermal management of wearable devices remains a significant challenge because of intrinsic leakage and rigidity issues. Therefore, this study develops a wearable phase-change film (FSPCF) that addresses these issues while providing high flexibility, superior solar thermal conversion efficiency and sensitive motion detection. The FSPCFs were fabricated using n-eicosane, vinyl-dimethylsiloxane, hydrosilicone oil and multiwall carbon nanotubes (MWCNTs) via salt-template-assisted and dip-coating methods. The interconnected 3D polysiloxane networks provided ample support for n-eicosane and effectively prevented liquid leakage during 500 thermal storage/release cycles. Increasing the amount of the deposited MWCNTs considerably improved the thermal conductivity of the FSPCF, from 0.314 W·m−1·K−1 (FSPCF-0) to 0.719 W·m−1·K−1 (FSPCF-1.2). The synthesised FSPCFs exhibited high thermal-energy-storage density (109.5–117.8 J/g), and a suitable phase-change temperature (about 36℃) for human thermal regulation and desirable thermal stability. Furthermore, FSPCF-added MWCNTs demonstrated excellent solar thermal conversion and storage efficiency (92.3%), making FSPCFs an attractive heat source for integration into wearable devices. Notably, the FSPCFs also demonstrated sensitive motion detection (GF = 46.3) and could monitor various human movements in real time, including curvature movements (bending of fingers, wrists, elbows, knees and neck), facial expressions and vocal vibrations. Overall, the developed film exhibits tremendous potential for use in the thermal management of wearable devices.