Grafting mechanism of poly(acrylic acid) from silica particles during the gelation process

Abstract

This study explores particle behaviors with regard to crosslinking mechanisms in an effort to understand the characteristics of hybrid gels. We focus on how particles provide a polymer grafting platform through radical polymerization, through interrogation at different gelation times. Silica-poly(acrylic acid) hydrogels were prepared by introducing gamma-ray-treated silica particles, which serve as both crosslinkers and initiators. The gelation and structural characteristics were investigated using dynamic light scattering, small-angle neutron scattering, microscopy, and spectroscopy measurements. We found that the incipient gels contain various types of particles stemming from the irregularity of polymer grafting. The particle sub-units were separated by pH controls from the other components generated from the gelation. In particular, the sub-units of core-shell particles were observed from the stage, which is close to the gel threshold. Polymer layers grafted to silica surface through chemical bonds show Si-O-C bonds, and they supported solution stability with stretched chains in aqueous solutions of high pH. The results suggest that sporadic grafting generates multiple components during gelation and could establish inhomogeneities in the consequent gels. This study provides details regarding the behavior of the silica particles during gelation and improves the understanding of the crosslinking process of nanocomposites.