ABSTRACT
The mechanical properties of most hydrogels (ionogels) are considerably affected by covalently cross-linked networks. However, the interactions between solvent/solvent molecules and solvent/polymer chains are usually ignored. Herein, a series of ultra-tough ionogels were prepared via a supramolecular solvent, halometallate ionic liquid, in which cations and coordinating anions form a 3D supramolecular network. The linear polymer chains are physically cross-linked with supramolecular solvents synergistically enhancing the strength (14.3â MPa), toughness (78â MJ m-3 ), and Young's modulus (55â MPa) of ionogels, effectively dispersing the stress concentration under load, and obtaining better fatigue resistance and higher fracture energy (198â kJ m-2 ). Furthermore, the reversible cross-linking enables green recovery and recycling of ionogels, simply by water. This strategy shows broad applicability based on a variety of supramolecular solvents and coordinatable polymers.
ABSTRACT
Ionogel-based flexible sensors are widely applied in wearable biomedical devices and soft robots. However, the abandoned ionic sensors are rapidly turning into e-waste. Here, we harness the porosity and the coordination of metal sites of metal-organic frameworks (MOFs) to develop physically crosslinked ionogels, which are composed of polymer chains that coordinate with the MOF metal sites. The covalent crosslinking of the host material transformed into reversible bond interactions that significantly enhance the mechanical properties of the MOF-ionogels. The obtained ionogels can endure an 11 000% stretch and exhibit Young's modulus and toughness of 58 MPa and 25 MJ m-3, respectively. In addition, the fracture energy is as high as 125 kJ m-2, outperforming most reported ionogels. Furthermore, the UiO-66-ionogels are fully recyclable and both the mechanical and electrical properties can be restored. The results of this work provide a new vision for the development of future "green" sensors.
