An investigation into the stability of aqueous films separating hydrocarbon drops from quartz surfaces

An investigation has been made on the stability of the thin aqueous film that separates a hydrocarbon droplet from a quartz plate immersed in an electrolyte solution. In the initial studies using dodecane, the ionic strength and pH of the bulk aqueous phase were altered to quantitatively determine the effects on film thickness and stability. Comparison of these results with calculations from DLVO theory provided an indication that electrostatic forces played the dominant role in the stabilisation of thin aqueous films. The experimental techniques were applied to study several oils approaching a quartz surface in salt solutions. In these studies, film collapse was facilitated by inclusion of asphaltene material into the hydrocarbon. This was suggested to be due to adsorption of asphaltene at the oil/water interface altering the surface potential. In the simple hydrocarbon systems, the transition of a thin film to an optically black film did not imply a change in the wettability condition, as drops could be detached cleanly from the quartz substrate to leave a water-wet surface. When asphaltene was present in the oil phase, film collapse was accompanied by apparent wettability alteration. Irrespective of reversibility considerations, film collapse was observed to produce a heterogeneous surface of brine and oil-contacted domains on the quartz surface. (C) 1999 Elsevier Science B.V. All rights reserved.