Study of water-in-oil thin liquid films: Implications for the stability of petroleum emulsions

The lifetimes, thicknesses, and thinning rates of water-in-diluted bitumen emulsion thin liquid films depend on solvent-to-bitumen ratio (S/B) and on the aromaticity of the solvent used. For aliphatic solvents, the emulsion film properties change abruptly at a well-defined dilution coinciding with the onset of asphaltene precipitation and previously observed critical S/B at which bulk emulsion properties change dramatically. Microscopic observations reveal that above critical S/B, water/oil interfaces become rigid and small asphaltene aggregates are formed. After some ageing time, larger secondary precipitates appear in the film. When the bitumen was diluted above critical S/B and precipitated asphaltenes were removed by centrifugation, we observed a significant increase in the equilibrium film thickness and stability. This counterintuitive finding is possibly due to a build-up of a multilayer at the water/oil interface, driven by poor solubility of asphaltenes in aliphatic solvent. The experiments were performed using the microinterferometric thin liquid film technique. The films were created from Athabasca bitumen diluted with mixtures of toluene and heptane at various toluene to heptane and solvent to bitumen ratios.