Stretchable dual nanocomposite hydrogels strengthened by physical interaction between inorganic hybrid crosslinker and polymers

Abstract Stretchable hydrogels have been developed by fabricating a dual nanocomposite structure by polymerization of hydrophilic monomers and sol-gel reaction of tetraethyl orthosilicate (TEOS) in the presence of Laponite. The mechanical enhancement of the hydrogels was markedly influenced by monomer structure and contents of TEOS and Laponite. The strong interaction between N-isopropylacrylamide (NIPAM) and inorganic hybrid crosslinker was examined by dyeing experiment, transparency and fluorescence measurement of Laponite/SiO2/monomer dispersions. This accounted for the excellent mechanical properties of Laponite/SiO2/PNIPAM dual nanocomposite hydrogel. Uniaxial tensile tests showed improved tensile property (elongation at break: 1845 ± 3.46%; fracture stress: 271.41 ± 6.26 kPa), and elastic modulus of the hydrogel significantly increased with TEOS contents and reached 26.69 ± 6.13 kPa at 10:1.0 of mLaponite:mTEOS. Fracture compression strength could reach 7.06 ± 1.25 MPa (fracture energy: 1185.53 ± 5.57 J m− 2), meanwhile it showed remarkable fatigue resistance. The embedded nano-SiO2 accounted for the significantly improved stiffness of the hydrogels. Moreover, the dual nanocomposite mechanism (the covalent bonding of SiO2 with Laponite and strong physical interaction of polymer chains with inorganic hybrid crosslinker) made a big contribution to the toughness of the gels. The noncovalent entanglements between SiO2 and polymer chains could promote both strength and elongation of the hydrogel, but the effect is not as notable as the covalent one.