Tough, multifunctional, and green double-network binary solvent eutectogel with in-situ generation of lignin nanoparticles based on one-step dual phase separations for wearable flexible strain sensors

Eutectogels have been applied to wearable flexible strain sensors as substitutes for hydrogels, organogels and ionic gels due to its superior ionic conductivity, non-volatility, and low cost. However, most of them are polymeric eutectogels with petroleum-based polymers without environmental friendliness, and the mechanical properties. And the electrical conductivity cannot be achieved at the same time, which hinder their practical application in the field of flexible electronics. Here in, a simple one-step strategy for the in-situ generation of lignin nanoparticles in polyvinyl (alcohol)/gelatin double cross-linked network by dual phase separations was proposed to fabricate multifunctional green binary solvent eutectogels. The deep eutectic solvents/water as a binary solvent inducing polyvinyl (alcohol) micro-phase separation and kraft lignin self-assembling to form lignin nanoparticles during the phase separation. The synergistic effect makes eutectogels with excellent room temperature solidification, multiple response, UV-shielding, antibacterial activity, water retention, anti-freezing, biocompatibility, recyclability, high mechanical properties (tensile strain of 574.068 ± 25.986% and strength of 3.248 ± 0.212 MPa), high conductivity of 2.042 ± 0.12 S/m and high sensitivity with a maximum gauge factor of 8.86. It can be applied to human motion health monitoring, micro-expression recognition and speech recognition, combining writing recognition with deep learning models, which proposes the research direction of sensor and human–machine interface complementing each other for recognition.