Molecular insights on the mechanical properties of double-network hydrogels reinforced by covalently compositing with silica-nanoparticles

Abstract

In this work, a novel TM-SiO2/PAM/PAA nanocomposite double network (DN) hydrogel with excellent mechanical performance was prepared, which combined the advantages of DN hydrogel and nanocomposite hydrogel. The triethoxyvinylsilane-modified SiO2 (TM-SiO2) nanoparticles are used as cross-linking agents, and are copolymerized with AM monomers to form the first network of nanocomposite materials. The nanocomposite was first swelled in an aqueous solution of AA monomer, and then a second network was introduced by polymerization of AA monomer. The effects of TM-SiO2 nanoparticles content and DN structure on the microstructure, tensile strain, and compressive strain of TM-SiO2/PAM/PAA nanocomposite DN hydrogel were investigated. The structure and mechanical properties of the hydrogel were compared with the pure PAM, pure PAA, and PAM/PAA DN hydrogels. The energy dispersive spectroscopy of Si element was used to explore the dispersion of nanoparticles in the network structure of nanocomposite DN hydrogel. The results show that the introduction of DN structure and nanoparticles can obtain a denser structure with smaller average pore size (From 475 μm to 70 μm). In particular, introducing 0.2 wt% − 0.8 wt% TM-SiO2 nanoparticles, the fracture tensile stress of the TM-SiO2/PAM/PAA nanocomposite DN hydrogel increased from 0.26 MPa to 0.43 MPa. The compressive stress of the TM-SiO2/PAM/PAA nanocomposite DN hydrogel increased from 4.93 MPa to 7.01 MPa at the compressive strain was 70 %. Moreover, the hydrogel containing 0.8 wt% of TM-SiO2 nanoparticles had higher strength than the others, and TM-SiO2 nanoparticles are dispersed well in the hydrogel. Molecular dynamics simulation is performed to investigate the interaction mechanism of hydrogel components and the stability of hydrogel system.