Dispersion and its mechanism of hydrophobic fumed silica particles in aqueous system

Abstract

Dispersions of hydrophobic fumed silica particles were investigated in various aqueous systems to understand its mechanisms. For this purpose, model systems are designed in a range of polar organic solvents with water, including various alcohols, polyethylene glycol and glycerin to change the hydrophobicity of the medium. Both hydrophilic and various hydrophobic fumed silica particles which have different surface properties were used as well

The effect of affinity between particles and mediums are studied by observing changes of rheological behaviours and microstructure of the dispersions. Hydrophilic fumed silica particles form stable dispersion with low viscosity in water and other solvents. On the other hands, water shows difficulties in dispersing hydrophobic fumed silica particles without other polar organic solvents presents in the medium with water. Hydrophobic fumed silica particles flocculate into colloidal gels in the mediums such as propyl alcohol in water. The extent of flocculation and gelation of the dispersions is different according to the hydrophobic alkyl chain length and number of OH of the polar organic solvents. Moreover, the alkyl chain lengths and concentrations of polar organic solvents in water both show influences on the extent of flocculation.