Methacrylic Acid Based Polymer Networks with a High Content of Unfunctionalized Nanosilica: Particle Distribution, Swelling, and Rheological Properties

The poor stability and tendency to agglomerate of unfunctionalized nano-SiO2 in the presence of ionic species presents a challenge for preparing poly(methacrylic acid)/nano-SiO2 nanocomposite (NC) hydrogels with desired strength and swelling capability. We proposed a facile and eco-friendly method for the preparation of PMAA/SiO2 NC hydrogels using unfunctionalized silica nanoparticles (NPs) in the form of a suspension. SEM and TEM analyses showed that the NP distribution in the polymer matrix highly depended on the particle concentration. At lower concentrations (up to 13.9 wt %), the NPs were uniformly dispersed as single nanoparticles. With an increase in NP concentration, homogeneously dispersed nanoscale aggregates were formed, while a further increase in the silica concentration led to the formation of homogeneous structures consisting of mutually interacting nanosilica particles coated with PMAA. Swelling experiments confirmed that the silica NPs behaved as adhesive fillers that interacted with PMA...