Self-healing, adhesive liquid metal hydrogels based on PNIPAM microgels for high-performance temperature and strain sensors†

Abstract

Conductive hydrogels have attracted much attention as candidates for flexible strain sensors. However, the preparation of multifunctional hydrogel sensors with excellent comprehensive performance is still a great challenge. In this study, a facile preparation method was used to prepare the conductive hydrogel MR/LM-PAAm-PEI (ML) by mixing PNIPAM microgels and gallium-based liquid metals. The hydrogel not only has excellent mechanical properties but also exhibits good temperature responsiveness and electrical properties, as well as efficient adhesion and excellent self-healing ability. The sensors of the ML hydrogel are capable of accurately and reproducibly recognizing handwriting and encrypted information and have excellent sensing ability as strain sensors (sensitivity GF value up to 5.45, ultra-fast response and recovery times of 160 ms and 170 ms, respectively, and a wide range of strain sensing up to 10–400%). The sensing mechanism of the hydrogel relies on changes in its internal structure when it is deformed or exposed to temperature variations. These structural changes lead to alterations in the conduction pathways within the hydrogel, which in turn triggers significant changes in the electrical signal. In particular, the sensors of the ML hydrogel have excellent thermal sensitivity and were used as temperature sensors over a wide range of 20–70 °C. The use of the sensor for finger movements to transmit Morse code messages has also been successful. This work offers prospects for the development of multifunctional strain sensors.