Eco-friendly, self-healing, and stretchable graphene hydrogels functionalized with diol oligomer for wearable sensing applications

Abstract

Graphene-based materials are of emerging interest; however, low stretchability limits their potential for wearable and sustainable electronics. Thus, this study presents the development of deformable and self-healing graphene hydrogels functionalized with polyurethane diol oligomer for wearable sensing applications. Controlling the loading of the oligomer, acting as a non-toxic plasticizer and providing abundant hydrogen bonds, is crucial to turn the functionalized hydrogels into a quasi-solid state with good stretchability and rapid healing ability (at room temperature). In sensing measurements, resistive-type sensors employing the functionalized hydrogels as the active channel show high responsiveness towards either small temperature changes (ΔT ∼ 0.2 °C near 25 °C) or the existence of ammonia and nitrogen dioxide gases at very low concentrations (0.7–20 ppm and 0.8–3.5 ppm, respectively). Notably, the ammonia detectability of our material is excellent in a wide relative humidity range (0–65 %). Besides, the sensors can be elongated to 30 %, and the healing ability of the hydrogels can recover the sensing capability of damaged sensors (about 90 % in 30 s). Overall, the obtained results suggest that our functionalized graphene hydrogels are promising for developing wearable sensing applications like e-skin and e-nose.