Highly transparent, self-healing and adhesive wearable ionogel as strain and temperature sensor

Abstract

Wearable strain, pressure, and temperature sensors have tremendous potential applications in human motion detection and personal healthcare monitoring. However, it is a challenge to design a flexible and wearable sensor which unifies multifaced properties, such as favorable adhesion, high transparency and stretchability, self-healing capability, and the ability to detect a change in strain, pressure or temperature with high sensitivity. Here, we resolve this long-standing mismatch through a physical crosslinking design. A stable ionogel is fabricated by facilely mixing ionic liquid (IL) with allyl monomers, and then initiating polymerization by UV light without covalent crosslinking. The obtained ionogel shows good self-healing capability and adhesion, excellent stretchability (2017%), high durability (1000 cycles at 50% strain), environmental tolerance (thermal stability and vacuum stability) and high transparency (92%, 1 mm). The assembled ionogel-based strain sensor exhibits a wide strain response range (600%) and excellent reproducibility (1000 cycles). More interestingly, the ionogel-based sensor can be assembled into a sensor for recognition of written strokes and a tapping sensor with high accuracy, providing a means for the transmission of secret information. Based on the temperature-dependent conductivity of IL, the ionogel is designed as a temperature sensor with a wide operating window (−20 to 120 °C), an ultralow detection limit (0.1 °C), and high sensitivity (4% °C⁻¹). By virtue of its remarkable sensing abilities in terms of strain and temperature, this ionogel-based sensor can not only detect the strain deformation caused by subtle changes in facial expression and large joint bending but also detect tiny changes in temperature, which suggest great promise in wearable devices and electronics.