In situ synthesis of poly(acrylic acid) physical hydrogels from silica nanoparticles

This paper introduces a versatile method to synthesize physical hydrogels by silica nanoparticle (SN) surface in situ polymerization. A series of poly(acrylic acid) chains were covalently grafted from the SNs that were treated with gamma-methacryloxypropyl trimethoxy silane. The entanglements among the grafted chains constructed the hydrogel networks and the SNs played the role of 'analogous crosslinking points'. The SNs were encapsulated by the grafted polymer chains and formed a 'core-shell' structure. It was found that the molecular weight of the grafted chains and the content and diameter of the SNs affected the hydrogel's properties. In comparison with chemically crosslinked hydrogels, the hybrid hydrogels exhibited excellent mechanical properties and could endure stress as high as 3.16 MPa and an elongation of 440% at a water content of 100 wt%. The gel-sol phenomenon confirmed that this hybrid hydrogel belonged to the physically crosslinked type.