The role of reduced graphene oxide as a "2D flexible crosslinking point" in composite hydrogels

The composite hydrogels are widely used in various research directions. How to improve the mechanical properties is one of the concerns of researchers. In this work, the mechanical properties of composite hydrogels with reduced graphene oxide (rGO), kaolin (KL), montmorillonite (MMT), and attapulgite (APT) as additives were compared. The morphology of polyacrylamide (PAM) composite hydrogel was observed by electron microscope, and the hydrogen bonding between inorganic additives and PAM chain in the hydrated samples were detected by IR. The rheological data (G('), G("), and tan delta) confirmed the beneficial effect of rGO as a two-dimension (2D) material on the mechanical properties of hydrogels. In the tensile-fracture experiments, the maximum tensile strain of PAM-rGO was 568% and the maximum tensile force was 1.18 N, both of which were larger than that of the clay-based composite hydrogel with the same mass concentration. Based on these experimental data, the response behavior of rGO in the process of hydrogel deformation was elucidated by the concept of "2D flexible crosslinking point," and the reason why PAM-rGO composite hydrogel had better mechanical strength was explained in detail.