Indirect method for preparing dual crosslinked eutectogels with high strength, stretchability, conductivity and rapid self-recovery capability as flexible and freeze-resistant strain sensors

Environmentally tolerant multifunctional eutectogel for highly sensitive wearable sensors

Flexible hydrogel sensors have found extensive applications. However, the insufficient sensing sensitivity and the propensity to freeze at low temperatures restrict their use, particularly in frigid conditions. Herein, a multifunctional eutectogel with high transparency, anti-freezing, anti-swelling, adhesive, and self-healing properties is prepared by a one-step photopolymerization of acrylic acid and lauryl methacrylate in a binary solvent comprising water and deep eutectic solvent (DES). The results from the molecular dynamics simulations and density functional theory indicate that the hydrogen bonds between DES and water mixtures possess better stability than those between water molecules. On the other hand, DES breaks down hydrogen bonds in water, providing eutectogels with excellent anti-freezing even at -60 °C. Cetyltrimethylammonium bromide is incorporated to establish stable hydrophobic interactions and electrostatic attractions with polymer chains in the eutectogel network, resulting in superior mechanical (elongation at break of 2890%) and anti-swelling (only 2% swelling in water over 7 days) properties. The eutectogel-based strain sensors exhibit remarkable sensitivity, achieving a gauge factor of up to 15.4. The multifunctional eutectogel sensors can monitor motion and transmit encrypted information at low temperatures, demonstrating considerable potential for applications in flexible electronics within low-temperature environments.

High Strength, Strain, and Resilience of Gold Nanoparticle Reinforced Eutectogels for Multifunctional Sensors

Eutectogels with inherent ionic conductivity, mechanical flexibility, environment resistance, and cost-effectiveness have garnered considerable attention for the development of wearable devices. However, existing eutectogels rarely achieve a balance between strength, strain, and resilience, which are critical indicators of reliability in flexible electronics. Herein, poly(sodium styrenesulfonate) (PSS)-modified gold nanoparticles (AuNPs) in eutectic solvents are synthesized, and PSS-AuNP reinforced polyacrylic acid/polyvinylpyrrolidone (SAu-PAA/PVP) eutectogel is successfully prepared. Through the coordination between AuNPs and the PAA/PVP polymer chains, the SAu-PAA/PVP eutectogel exhibits significantly enhanced tensile strain (946%), mechanical strength (3.50 MPa), and resilience (85.3%). The high-performance eutectogel was demonstrated as a flexible sensor sensitive to strain and temperature, and the AuNPs provided near-infrared sensing capabilities. Furthermore, SAu-PAA/PVP eutectogel inherits the benefits of ES, including anti-drying and anti-freezing properties (-77 °C). Moreover, the eutectogel is microstructured using a simple molding method, and the resulting hierarchical pyramid microstructured eutectogel functions as ionic dielectric layer in a pressure sensor. This sensor exhibits high sensitivity (37.11 kPa-1), low detection limit (1 Pa), a fast response rate (36/54 ms), and excellent reproducibility over 5000 cycles, making them reliable and durable for detecting small vibrations, with potential applications in precision machinery, aerospace, and buildings.

Self-Healing and Antifreezing/Antidrying Conductive Eutectohydrogel-Based Biosignal Monitoring Multisensors with Integrated Supercapacitor

A novel self-healing and antifreezing/antidrying conductive eutectohydrogel, ideal for wearable multifunctional sensors and supercapacitors, is reported. Conductive eutectohydrogel with self-healing and facilely tunable mechanical performance is obtained by incorporation of trehalose and phytic acid as reversible cross-linkers into a polyacrylamide network, forming the dynamic hydrogen bonding and electrostatic interactions. Furthermore, combined use of deep eutectic solvent with water ensures the air stability as well as the antifreezing/antidrying characteristics. The synthesized eutectohydrogel exhibits a self-healing efficiency of 90.7% after 24 h at room temperature, Young's modulus of 140.9 kPa, and strain at break of 352.8%. With the eutectohydrogel as a versatile platform, self-healing strain and temperature sensors, electrocardiogram electrodes, and supercapacitor are fabricated, recovering the device performance after self-healing from complete bisection and exhibiting stable performance over a wide temperature range from -20 to 50 °C. With a vertically integrated patch device of supercapacitor and strain sensor attached onto skin, various body movements are successfully detected using the energy stored in the supercapacitor, without performance degradation even after self-healing from complete bisection of the full patch device. This work demonstrates high potential application of the synthesized eutectohydrogel to flexible wearable devices featuring durability and longevity.

Cellulose-reinforced highly stretchable and adhesive eutectogels as efficient sensors

A cellulose-reinforced eutectogel was constructed by deep eutectic solvent (DES) and cotton linter cellulose. Cellulose was dispersed in the ternary DES consisting of acrylic acid, choline chloride and AlCl3·6H2O. The photoinitiator was then introduced into the system to in situ polymerize acrylic acid monomer to form transparent and ionic conductive eutectogels while keeping all the DES. The crosslinks formed by Al3+ induced ionic bonds and reversible links formed by hydrogen bonds give the eutectogels high stretchability (3200 ± 200 % tensile strain), self-adhesive (52.1 kPa to glass), self-healing and good mechanical strength (670 kPa). The eutectogels were assembled into sensors and epidermal patch electrodes that demonstrated high quality human motion sensing and physiological signal detection (electrocardiogram and electromyography). This work provides a facile way to design flexible electronics for sensing.