Stability and rheological properties of silica suspensions in water- immiscible liquids

This paper overviews silica suspensions in water-immiscible liquids, with an emphasis on their dispersion stability and rheological properties as a function of the surface characteristics of silica powders at lower silica volume fractions, ϕ, than 0.1. In addition, a critical review is presented the manufacturing process of silica powder by considering their microstructures. Hydrophilic fumed silica powders are in a gel state at lower ϕ than hydrophobic fumed silica powders in water-immiscible liquids. The interaction between the surface silanol groups is dominant in the former; whereas in the latter, the mutual interaction between the surface hydrophobic moieties and the dispersion media is favored. Moreover, the dynamic moduli of the hydrophobic fumed silica suspensions strongly depend on the mutual interaction between the hydrophobic moieties and the dispersion media. Their magnitudes become larger as mutual interactions increase. In addition, the effects of the adsorption of polymers and non-adsorbing polymers on the dispersion stability and rheological behavior of hydrophilic or hydrophobic fumed silica suspensions are discussed, by considering their small-angle neutron scattering (SANS) curves. The precipitated silica suspensions are more compact and form smaller microstructures than the fumed silica suspensions and their gels correspond to the weak-link gel.