Thermochromic and conductive hydrogels with tunable temperature sensitivity for dual sensing of temperature and human motion

Abstract

Skin-like body sensors have important applications in soft-bodied intelligent robots, electronic skins, and medical health monitoring. Accurate sensing of pressure and temperature are two core elements of skin-like sensors that mimic skins. Skin-like sensors convert sensed external stimuli such as pressure and temperature into electrical signals, enabling visual monitoring of external environmental stimuli. However, there are very limited reports on hydrogel-based and dual stimuli-responsive (strain/temperature) sensors. To this end, we report a highly flexible strain/temperature dual stimuli-responsive sensor based on poly(acrylamide) (PAAM) hydrogels. Our prepared conductive ionic hydrogels are endowed with the ability to undergo phase changes at different temperatures by introducing inexpensive and stable sodium dodecyl sulfate (SDS) thermotropic phase-change units, which can turn from opaque to transparent within 10 s when temperature is increased, and to opaque again when temperature is decreased. In this study, we have succeeded in producing a dual-responsive multifunctional ionic conductive hydrogel (SN-PAAM) that is responsive to temperature/strain dual stimuli and has excellent mechanical properties: high tensile strength (581 kPa), extra long elongation (1836%), high sensitivity (GF = 1.62 to 2.46), and short response time (120 to 130 ms). To the best of our knowledge, these combined functions are not achievable with conventional strategies. Therefore, the hydrogels developed in this research could have good prospects for different applications such as flexible wearable devices, skin-like sensors, visualization of bionic skins, dual response interactive devices, and in the field of anti-counterfeiting and encryption.