Solvent-induced in-situ self-assembly lignin nanoparticles to reinforce conductive nanocomposite organogels as anti-freezing and anti-dehydration flexible strain sensors

Despite the remarkable progress in efforts to fabricate flexible and wearable sensors based on the conductive hydrogels has been witnessed in recent years, the traditional conductive hydrogels still suffer from poor mechanical properties and intrinsic instability owing to the inevitable freeze at low temperature and water evaporation at room temperature, severely limiting their practical applications. Herein, we developed a robust and conductive lignin-based nanocomposite organogel with extreme temperature tolerance and long-lasting moisture, which is prepared in a binary-solvent system composed of dimethyl sulfoxide (DMSO) and water. Notably, the incorporation of DMSO/H2O binary solvent facilitates the transformation from lignin macromolecules into nanoparticles by self-assembly method, leading to the significant mechanical reinforcement of the obtained polyvinyl alcohol-lignin nanoparticle (PVA-LN) organogel. Meanwhile, the formation of a large amount of hydrogen bonds between DMSO and water molecules prevented the generation of ice crystals, and the water evaporation was hindered simultaneously. Thus, the PVA-LN organogel exhibited incredible freezing tolerance (-80 °C) and remarkable long-lasting moisture (88% weight retention after 7 days), remaining stable mechanical flexibility and electrical conductivity in a wide temperature range. In addition, profited from the high strain sensitivity, fast response time, and excellent stability, the PVA-LN organogels were applicable to be assembled into flexible strain sensors to detect large human motions and subtle physiological signals even at extreme environments. It is envisioned that this work opens up a new prospect for the design of the stretchable biomass-based hydrogels with strain-sensitive properties for potential applications in flexible wearable electronics and healthcare monitoring in a broad temperature range.