The Effect of Aqueous Dispersions of Functionalized Silica Particles on Interfacial Tensions of Water/Oil/Solid Systems

Interfaces in systems formed by water/oil/solid are present, for example, in oil reservoirs or cleaning fat-impregnated solids with surfactants. Surfactants modify the interfacial tensions between these phases and remove oil as an emulsion. Dispersions of particles with different wettability also act on these interfaces through the mechanism described by Pickering¹. In this work, aqueous dispersions of functionalized silica particles, prepared by the simultaneous hydrolysis of tetraethylorthosilicate (TEOS), trimethoxy(n-octyl)silane (TMOcS), and (3-aminopropyl)triethoxysilane (APTES) in different proportions, were added to the aqueous phase of a system formed by: water droplet/mineral oil/solid with hydrophilic or hydrophobic surface. Variations in the contact angle at the water/oil/solid interfaces evaluated the effect of dispersions on interfacial tensions. Dispersions of functionalized silica particles with 20% aminopropyl groups and 80% n-octyl groups did not significantly modify the contact angle for systems with hydrophilic or hydrophobic solids, as well as, hydrophilic silica particles prepared by TEOS hydrolysis. Dispersions of functionalized silica particles prepared by simultaneous hydrolysis of TEOS and APTES decrease the contact angle for the hydrophobic solid in the same way as the addition of surfactant solutions. The decrease in the contact angle suggests that functionalized silica particles, prepared with TEOS and APTES, are wetted by both the aqueous and oil phases simultaneously; particles prepared with APTES and TMOcS are wetted only by the oil phase; and hydrophilic silica particles are wetted only by water.