Weak-gel formation in dispersions of silica particles in a matrix of a non-ionic polysaccharide: structure and rheological characterization

Abstract

Oscillatory and steady shear rheological methods as well as scanning electron microscopy were used to characterize silica(SiO2)/galactomannan dispersions. Particle loading and surface charge are found to strongly influence the composite structure and dynamics. When the particles were added above a minimum concentration, a sol-gel transition was induced. The SiO2/polysaccharide dispersions exhibited significant non-linearities, especially under ionic conditions that favor interparticle and particle-polysaccharide interactions, characterized by strong shear-thinning, diverging viscosities at low shear rates, apparent yield stress and high strain sensitivity. The mechanical spectra for the composite systems suggest that stress relaxation of these composites is effectively arrested by the presence of silica nanoparticles. Microstructural analysis revealed an ordering of the silica particles around the polymer chains. Polysaccharide chains act as templates for particle clustering leading to the formation of a particle-mediated transient biopolymer network, with particle clusters hindering polymer mobility and enhancing junction zones within the network.