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 th at separates a hydrocarbon droplet from a quartz plate immersed in an elect rolyte solution. In the initial studies using dodecane, the ionic strength and pH of the bulk aqueous phase were altered to quantitatively determine t he effects on film thickness and stability. Comparison of these results wit h calculations from DLVO theory provided an indication that electrostatic f orces 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 fac ilitated 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 tra nsition 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 qua rtz substrate to leave a water-wet surface. When asphaltene was present in the oil phase, film collapse was accompanied by apparent wettability altera tion. Irrespective of reversibility considerations, film collapse was obser ved to produce a heterogeneous surface of brine and oil-contacted domains o n the quartz surface. (C) 1999 Elsevier Science B.V. All rights reserved.