Covalently cross-linked layered double hydroxide nanocomposite hydrogels with ultrahigh water content and excellent mechanical properties

Hydrogels with their intriguing three-dimensional (3D) cross-linked networks have found multiple applications. However, conventional chemically cross-linked hydrogels are inevitably facing with severe problems such as mechanical weakness and brittleness. In this context, we present a new class of covalently cross-linked nanocomposite (NC) hydrogels based on tris(hydroxymethyl) amino-methane (Tris)-modified layered double hydroxides (LDHs). Reaction of the resultant Tris-LDHs and acryloyl chloride gives Acryloyl-LDHs which can serve as cross-linkers for construction of 3D hydrogel networks. The resulting covalently cross-linked NC hydrogel can be stretched to more than 18 times of its original size and compressed at 90% deformation without rapture. Moreover, such hydrogel can retain as much as 97% of water, and the compressive modulus can reach to 543.7 kPa at a very low cross-linking density of 0.377 molm-3. The excellent mechanical performances are attributed to the flexible polymer chains obtained in NC hydrogels and the necking phenomenon caused by the Tris-LDHs. This work provides a new method for development of stable and mechanically strong hydrogels with high water contents.