Hybrid nanocomposite hydrogels with high strength and excellent self-recovery performance

Abstract

Polymer nanocomposite hydrogels (NC gels) have been intensively investigated for applications in academic and industrial fields. In the present work, hybrid cross-linked polyacrylamide (PAAm)/LAPONITE® hydrogels were synthesized by in situ free radical polymerization using LAPONITE® nanoplatelets and N,N-methylenebisacrylamide (MBA) as physical and chemical crosslinkers, respectively. We aimed to make clear the synergistic effect of physical and chemical crosslinking on the mechanical properties, self-recovery, fatigue resistance and self-healing performances of hybrid PAAm/LAPONITE® NC gels. The effects of LAPONITE® and chemical cross-linker concentration on the mechanical properties of the physical and hybrid NC gels were investigated in details. It was found that the fracture stress and fracture energies of hybrid NC gels decreased sharply as the chemical crosslinker (MBA) concentration became larger than 0.05 mol% of monomer. With a very small amount of chemical crosslinker, the hybrid NC gels exhibited improved tensile properties, large hysteresis and good self-recovery performances. The best tensile properties of hybrid NC gels in this study were σ_f of 0.45 MPa, ε_f of 50.63 mm mm⁻¹, E of 72.64 kPa and W of 9.81 MJ m⁻³, which were much better than those of physical NC gels and pure chemical gels. However, it was also revealed that there was a negative effect from chemical crosslinking on the fatigue resistance and self-healing properties of NC gels. A deformation and recovery mechanism was also proposed. We believe this work will provide better understanding about the relationship of network structure and properties for hybrid NC gels.