Reinforcing effect of graphene oxide on mechanical properties, self-healing performance and recoverability of double network hydrogel based on κ-carrageenan and polyacrylamide

Double network (DN) hydrogels are considered as one of the toughest group of materials with unique structural platforms which exhibit a combination of different mechanical properties into a single material. However, it is highly favorable yet challenging to design a hydrogel that combines required levels of mechanical properties as recovery efficiency, toughness, stretchability, and fatigue resistance with self-healing property for potential applications. Here we successfully synthesize a new kind of kappa-carrageenan (kappa-Car)/polyacrylamide (PAm)/graphene oxide (GO) nanocomposite double network (NCDN) hydrogel with desired mechanical properties and self-healing performance by using GO as the network crosslinking reinforcement. As compared to the DN hydrogel without GO nanosheets, the NCDN hydrogel containing an optimized amount of 0.3 wt% GO exhibited excellent mechanical properties (compression strength: 21.7 MPa, failure tensile stress: 0.64 MPa, failure tensile strain: 2398% and fracture energy: 5.7 MJ/m 3 ), significant hysteresis (0.98 MJ/m(3) at lambda = 10), enhanced toughness recovery (similar to 97.23% at 90 degrees C and similar to 67.07% at room temperature), and good fatigue resistance simultaneously. This could be explained in terms of the synergistic effect of the reversible interactions induced by bridging of the GO nanosheets between the kappa-Car and PAm networks. This not only allowed an additional load transfer between the two networks but also had a great contribution to energy dissipation of the hydrogels through desorption of anchored polymer chains from the surface of the GO together with GO amplification effect on molecular orientation. Moreover, multi-reinforcing action of GO and thermo-reversible property of the kappa-Car network enabled the NCDN hydrogel to exhibit self-healing capability, thermo-responsive property, and remarkable thermal stability at elevated temperature. The results of this work provided a great insight into understanding the correlation between microstructure and mechanical performance of hydrogels and extend hydrogel applications, especially for the stimuli-responsive load-bearing.