On water-in-oil emulsions stabilized by fine solids

The stability of water-in-oil emulsions stabilized by fine solids with different hydrophobicities were studied with model organic solvents, such as light mineral oil (Bayol-35), decane and toluene. The fine solids used in this study include kaolinite clay particles treated with asphaltenes, hydrophilic and hydrophobic colloidal silica, hydrophobic polystyrene latex microspheres, as well as fumed silica dry powders treated with silanization. Experimental results showed that hydrophilic colloidal silica could only stabilize oil-in-water emulsions for a short period of time. If hydrophobic particles (colloidal silica or polystyrene latex microspheres) were suspended in the aqueous phase prior to emulsification, they could only produce oil-in-water emulsions. Only hydrophobic particles suspended in organic phase prior to emulsification could stabilize water-in-oil emulsions. The size of the water droplets in emulsion was as small as 2 mum when the solids were 12 nm in diameter. The stability of the produced emulsions depended on the hydrophobicity of the particles. Only particles with intermediate hydrophobicity could produce very stable water-in-oil emulsions, and in some cases the volume of the produced emulsions was triple that of water present in the system. (C) 2001 Elsevier Science B.V. All rights reserved.