Aggregation of silica particles in non-aqueous media

The aggregation of micron-sized silica particles in non-aqueous (i.e. hydrocarbon) media was examined on both the macroscopic and microscopic scales. The silica surfaces were either “clean” or “treated” (i.e. with irreversibly adsorbed materials from Athabasca bitumen); the hydrocarbons were mixtures of toluene and heptane at various ratios (to allow for different degrees of “aromaticity” in the solvent). On the macroscopic scale, gravity settling of the silica beads in non-aqueous media was monitored, and particle–particle interactions were characterized semi-empirically by the initial rates of sedimentation. On the microscopic scale, adhesive forces between individual glass spheres were directly measured using the microcantilever technique (again, in non-aqueous liquids). It was found that, for clean silica spheres, the settling rates of the suspensions were relatively insensitive to the interparticle adhesive forces. This is in contrast to the case for treated silica beads, where strong correlation was observed between the settling rate and particle–particle adhesion. These findings may have important relevance to the commercial “paraffinic froth treatment” process.