writer：Guorong Gao, Gailai Du, Yajun Cheng, and Jun Fu*
keywords：double network hydrogel, clay nanorods, nanocomposite, toughness, chain adsorption
source：期刊
specific source：J. Mater. Chem. B, 2014, 2, 1539-1548.
Issue time：2014年

Polymer hydrogels with superior strength and toughness are potential candidate materials for the replacement or engineering of load bearing tissues. This manuscript reports on novel tough nanocomposite hydrogels with unusual energy dissipation mechanism based on both covalent and physical interactions between clay nanorods and polymer chains. Attapulgite (ATP) nanorods grafted with vinyl groups on the surface served as macro-crosslinkers to copolymerize with 2-acrylamido-2-methylpropane-sulfonic (AMPS) to form a nanocomposite first network, which subsequently hosted the polymerization of acrylamide (AAm) monomers to generate a novel nanocomposite double network (DN) hydrogel. The morphology, swelling behavior, compressive properties of the ATP-grafted DN hydrogels were investigated as a function of ATP content (CATP), in comparison with the ATP-filled DN gels. With the clay content between 0.1 wt% and 1.0 wt%, the nanocomposite hydrogels did not fracture up to a compressive strain of 98%, exhibiting an initial modulus (E) up to 0.36 MPa, a compressive strength higher than 65.7 MPa, and a work to fracture (or fracture energy) higher than 2.6 MJ m-3, in comparison to 0.19 MPa, 18.6 MPa, and 1.1 MJ m-3 for the conventional DN gels. Cyclic loading-unloading tests showed abnormal residual energy dissipation although the rigid PAMPS network had fractured. Such viscous energy dissipation decayed during cyclic loading and could be restored depending on time and temperature. This is related to the reversible desorption-re-adsorption of polymer chains from the clay surface. Possible reinforcing and fracture mechanisms are discussed.