Highly Stretchable, Repairable, and Tough Nanocomposite Hydrogel Physically Cross‐linked by Hydrophobic Interactions and Reinforced by Surface‐Grafted Hydrophobized Cellulose Nanocrystals

Highly stretchable, repairable, and tough nanocomposite hydrogels are designed by incorporating hydrophobic carbon chains to create first-layer cross-linking among the polymer matrix and monomer-modified polymerizable yet hydrophobic nanofillers to create second-layer strong polymer-nanofiller clusters involving mostly covalent bonds and electrostatic interactions. The hydrogels are synthesized from three main components: hydrophobic monomer DMAPMA-C18 by reacting N-[3-(dimethylamino)propyl]methacrylamide] (DMAPMA) with 1-bromooctadecane, monomer N,N-dimethylacrylamide (DMAc), and monomer-modified polymerizable hydrophobized cellulose nanocrystal(CNC-G) obtained by reacting CNC with 3-trimethoxysily propyl methacrylate. The polymerization of DMAPMA-C18 and DMAc and physical cross-linking due to the hydrophobic interactions between C18 chains make DMAPMA-C18/DMAc hydrogel. The additional introduction of CNC-G brings more interactions into the final hydrogel (DMAPMA-C18/DMAc/CNC-G): the covalent bonds between CNC-G and DMAPMA-C18/DMAc, hydrophobic interactions, electrostatic interactions between negatively charged CNC-G and positively charged DMAPMA-C18, and hydrogen bonds. The optimum DMAPMA-C18/DMAc/CNC-G hydrogel exhibits excellent mechanical performance with elongation stress of 1085 ± 14 kPa, strain of 4106 ± 311%, toughness of 3.35 × 104 kJ m-3 , Young's modulus of 844 kPa, and compression stress of 5.18 MPa at 85% strain. Besides, the hydrogel exhibits good repairability and promising adhesive ability (83-260 kN m-2 toward various surfaces).