Subzero fast self-healing and adhesive violet phosphorene incorporated sodium alginate-based hydrogel as strain sensors.

Hydrogels are promising materials for wearable electronic devices. However, maintaining the high sensitivity, self-healing, and excellent adhesion of hydrogels at subzero temperatures remains a challenge. The violet phosphorene-polydopamine hybrid (VP-PDA) was introduced into poly (vinyl alcohol)/ethylene glycol/sodium alginate/sodium tetraborate matrix to achieve an anti-freezing hydrogel with high strain sensitivity, extremely high stretchability (3539 %), rapid self-healing capability, and high adhesion even at -60 °C. The hydrogel-based strain sensor has been demonstrated to be significantly enhanced (especially at high strain, GF = 38.83 at 3000 % strain) by the introduction of VP with unique mechanical properties, accurately detecting different strains with quick response (<100 ms) during human activities (including finger flexion, wrist and elbow activity, walking) even at -60 °C. The dissipated energy and maximum stress of the hydrogel were detected to be stable after 1st cycling, consistent with its excellent cycling stability. The mechanical strength of the hydrogel was found to be rapidly self-healed in 5 min (healing efficiency 99.5 %) at room temperature, 15 min (healing efficiency 90.2 %) at -60 °C. The conductivity of the hydrogel was found to be self-healed in 1.1 s after cutting. This work provides a viable path to produce subzero self-healing and adhesive multifunctional hydrogel-based wearable sensors.