A flexible nanoparticle structured temperature sensor with high reproducibility and ultrafast response speed enabled by thermal expansion coefficient regulation and thermal conductivity enhancement
Peng Wang, Lingrui Meng, Guifen Sun, Wei Yu, Chuizhou Meng
Abstract
Temperature is a key physiological parameter to reflect the wearer's activity and health status, but quick and accurate temperature sensing in complicated skin-attaching condition remains challenging. Herein, we develop a flexible temperature sensor by constructing one reduced graphene oxide (rGO)/manganese dioxide (MnO 2 ) nanoparticle-composited Nomex/thermoplastic polyurethane (TPU) thermoresistive temperature sensing layer encapsulated between two eutectic Gallium-Indium (EGaIn) nanoparticle-embedded Polydimethylsiloxane (PDMS) thermally conductive layers. The temperature sensing layer exhibits an almost zero thermal expansion coefficient of ∼0.02 × 10 −3 K −1 through elaborate content matching of Nomex and TPU with opposite thermal expansion behaviors for accurate temperature sensing, and the encapsulation layer possesses high thermal conductivity of ∼0.34 W m −1 K −1 because of sufficient compositional addition of fine EGaIn particles for quick thermal responsiveness. The sensor shows excellent linearity with temperature coefficient of resistance of −1.1% °C −1 , low detection limit of discerning a 0.5 °C minor change, and good sensing stability within a detection range of up to 70 °C. Due to the strong bonding and hermetical sealing of PDMS, the developed sensor also exhibits the advantage of inertness to mechanical flexibility and moisture water. Practical skin-attaching temperature sensing applications of the sensors for monitoring of human activity and detection of finger touching gesture and even healing of mouse wound are well demonstrated.