“Deep Eutectic Solvent-in-Water” Hydrogels Enable High-Performance Flexible Strain Sensors for Electronic Skin with a Wide Operating Temperature Range

Abstract

Conductive hydrogels have become one of the hot topics in flexible strain sensors owing to excellent biocompatibility, attractive mechanical flexibilities, and conductive properties. However, the time-consuming preparation of hydrogels and their unsuitable properties limit their application in low-temperature environment and high temperatures. Here, a new class of “deep eutectic solvent-in-water” hydrogels (DIWHs) is reported for the first time through a one-step gelation process in situ without solvent displacement, fabricated by combining a hydrogel with deep eutectic solvent (DES). The DIWH is constructed using a dynamic oxidation and coordination system composed of sodium lignosulfonate (Ls) and Fe3+. The effect of DES and the optimal mass ratio of water and DES on the hydrogel properties was synthetically investigated. The addition of DES not only shortens the polymerization time to 8 s and enhances the mechanical properties of the hydrogel but also provides some unique properties. For example, the addition of DES gives the gels greater self-healing ability and antibacterial properties. When the mass ratio of water to DES was 1:3, excellent antifreezing and antidrying properties were imparted to the gel, and the elasticity of the hydrogel was maintained even at −80 °C or stored at 60 °C for 7 days. Furthermore, the hydrogel exhibited strong interfacial adhesion to natural and synthetic materials (up to 60 kPa on glass) due to the presence of Ls with a catechol structure. In conclusion, this work stimulates more interest in the sustainable and high-value utilization of DES and fully demonstrates the advantages of this new easy-to-prepare coacervation gel for sensing.

Recent Progress in Bioinspired Design Strategies for Freeze Resistant Hydrogel Platforms toward Flexible Electronics

“…Lyu reported a novel strategy for the fast fabrication of "deep eutectic solvent-in-water" hydrogels (DIWHs) constructed by a dynamic oxidation-coordination system of sodium lignosulfonate (Ls) and Fe 3+ . 162 Introducing DEs contributes to expediting the polymerization process to just 8 s and provides reinforced mechanical property. Additionally, the presence of a DES consisting of betaine and Gly not only endows the gels with superior self-healing but also exhibits impressive antifreeze behavior (−80 °C) and resistance to drying (60 °C for a week).…”

“…The second method to fabricate eutectogel utilization of DESs as solvents is within an independent polymerization network. ,− As illustrated in Figure b, Liu at al. presented a gradient-responsive cross-linking strategy for preparing a highly stretchable and reconfigurable thermoplastic engineering eutectogel with choline chloride/ethylene glycol (ChCl-EG) as the deep eutectic solvent (DES) .…”

“…Lyu reported a novel strategy for the fast fabrication of “deep eutectic solvent-in-water” hydrogels (DIWHs) constructed by a dynamic oxidation-coordination system of sodium lignosulfonate (Ls) and Fe 3+ . Introducing DEs contributes to expediting the polymerization process to just 8 s and provides reinforced mechanical property.…”

Fish Scale Biomimetic Multifunctional Antifreeze Organogel for Flexible Strain Sensor Applications

“…17 Lignin is the most abundant natural aromatic polymer 18 and has great potential in the field of functional materials. 19,20 Compared to bulk lignin particles, lignin nanoparticles have a smaller size with a larger specific surface area. When it is mixed with other polymers, the nanoparticles can interact closely with the polymer and distribute evenly in the matrix, which can increase the mechanical properties, thermal stability, and barrier properties of the lignin-based composites.…”

“…Lignin is the most abundant natural aromatic polymer and has great potential in the field of functional materials. , Compared to bulk lignin particles, lignin nanoparticles have a smaller size with a larger specific surface area. When it is mixed with other polymers, the nanoparticles can interact closely with the polymer and distribute evenly in the matrix, which can increase the mechanical properties, thermal stability, and barrier properties of the lignin-based composites. , For example, when the hydrogel is subjected to external force, the lignin nanospheres can effectively dissipate energy as a “sacrificial building”, maintain the stress of the internal network of the gel, and store energy, thus enabling the hydrogel to exhibit excellent mechanical properties. − This type of hydrogel has excellent mechanical properties, but the water in the hydrogel network is inevitably frozen below zero and evaporated at high temperatures, resulting in a significant decrease in its mechanical properties and affecting the applications of hydrogels. , …”