Stretchable, healable, and weldable vitrimer ionogel for ionotronic applications

The ionogels represents a class of materials consisting of ionic liquid confined in a polymer network. The mobile ions provide ionic conductivity while the polymer network enables flexibility and stretchability. They can exhibit healing, welding, reshaping, and recycling abilities when they are gifted with vitrimer properties, which make them promising candidates for sustainable soft electronics. Herein, vitrimer ionogel based on transesterification was synthesized via the epoxy ring-opening reaction with carboxylic acids of functionalized poly (ethylene glycol) (PEG) and triglycidyl ether crosslinkers in the presence of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm TFSI). The ionogel with 50 wt% EMIm TFSI exhibits good maximum strain (300 %), low elastic modulus (60 kPa) and high conductivity (2.6 x 10-4 S cm- 1), owing to the plasticizing effect and the introduction of mobile ions. Also, the presence of EMIm TFSI increases the chain mobility, overcoming the dilution effect and consequently facilitating the transesterification reaction of exchangeable beta-hydroxy ester linkages. Thus, the ionogel shows fast network rearrangement and full recovery of both tensile strength and conductivity properties. The ionogels were applied as strain sensor, soft electrode, and ionic cable, respectively. When used as a piezoresistive strain sensor, the ionogel exhibits high sensitivity (Gauge factor = 2.8), low hysteresis (3 %), low response time delay of 0.5 s and fully recovered its performance after healing from mechanical damage. In addition, the ionogel was applied as electrodes for a dielectric elastomer actuator, the ionogel can be welded onto an elastomer containing the same exchangeable beta-hydroxy ester linkages, for the fabrication of multilayer devices. which generated 12 % areal strain under a 42.5 MV/m electrical field. Second, a self-healable ionic cable was fabricated from this multilayer structure. It can transmit music signals and maintain the performance during stretching.