Particle-stabilized emulsions:: Effect of heavy crude oil components pre-adsorbed onto stabilizing solids

Model emulsions stabilized by means of silica nanoparticles have been investigated. The effect of the modification of the particle surface has been monitored using infrared (IR) spectroscopy, contact angle measurements and zeta potential measurements. It is shown how coating of the nanoparticles with asphaltenes and resins will modify the stabilization profile compared to that obtained with no coating. The stabilization efficiency was greatly enhanced by adsorption of crude oil components onto very hydrophilic or very hydrophobic silica. Possible stabilization mechanisms have been discussed. We have demonstrated catastrophic phase inversion of emulsions stabilized by particles with intermediate wetting properties, induced by simply increasing the volume of the disperse phase. In all cases, the stability to gravitational induced separation (coalescence) passes through a minimum approaching inversion in line with a maximum in drop size of the disperse phase. Transitional phase inversion from o/w to w/o emulsion type can be achieved by modifying of the hydrophilicity of the particles, either by silylation or by a controlled coating with heavy components from crude oil. The relevance of this study for real petroleum systems is discussed. (c) 2005 Elsevier B.V. All rights reserved.