Super strong and tough anisotropic hydrogels through synergy of directional freeze-casting, metal complexation and salting out

Strong and tough ionic conductive hydrogel is one of the key raw materials for the development of high-performance flexible electronic products. However, it is still challenging to prepare ionic conductive hydrogel materials with the integration of ultra-high mechanical strength, extremely high toughness and ionic conductivity. In this work, a simple strategy is proposed to prepare super strong and tough hydrogels through multi-length scale synergistic strengthening. The directional freeze-casting would endow hydrogels with good anisotropic structure at the micro-scale and the post-treatment of soaking in the saturated Na3Cit and Al2(SO4)3 composite solution would introduce metal complexation and chain entanglement to realize network structure densification at the sub-micro and nano-scale. These effects have been proven to be positive and synergistic, which can significantly increase the tensile strength, toughness and Young's modulus of the poly(vinyl alcohol)/carboxymethyl chitosan (PVA/CMCS) hydrogel. The optimum tensile strength, toughness, Young's modulus and tear energy of PVA/CMCS/Na3Cit/Al2(SO4)3 hydrogel reach 25.9 MPa, 90.9 MJ/m3, 422.6 MPa and 118.2 MJ/m2. This super strong and tough conductive hydrogel was assembled into a sensor and combined with Morse code to realize information transmission, encryption and decryption. This work provides a new scheme for the preparation of ultra-strong ionic conductive hydrogel for flexible electronics.