Effect of Viscosity on the Thin-Film Drainage between Bitumen and a Hydrophobic Silica Wafer

The drainage of the thin liquid film between a high-viscosity droplet and a solid surface or two approaching droplets is crucial in many industrial applications. For example, in oil sand extraction, the viscosity of bitumen significantly affects the liberation and aeration stages. However, previous studies rarely considered the effect of the bitumen viscosity on the dynamic thin-film drainage. In this study, we used the dynamic force apparatus (DFA) to study the initial film drainage process between a bitumen drop with a high viscosity compared to the surrounding aqueous solution and a hydrophobic silica wafer in 10 mM NaCl solution at pH 8.5 with a Reynolds number ranging from 0.27 to 3.8. The film drainage process of bitumen with comparable viscosity to the aqueous phase could be well-predicted by the Stokes-Reynolds-Young-Laplace model. However, the film drainage between bitumen with high viscosity and silica would form a much thinner dimple, followed by a film with a pointy-shaped center and a change of curvature at a radius of around 300 mu m. The addition of different types of solvent or increasing the experimental temperature would not affect the initial stage of dimple formation. A higher approach velocity and a smaller interfacial tension would result in a more pronounced dimple, but this effect would become minor when the bitumen viscosity is high enough. The initial height of dimple formation between bitumen with different viscosities and a hydrophobic surface could be perfectly predicted by the analytical formula derived using pure oil and a hydrophilic surface, h(d) = 0.5R root Ca-f/(1 + 2Ca(d)). It was also shown that a lower bitumen drop approach velocity, a higher bitumen/water interfacial tension, and a smaller bitumen viscosity would facilitate bitumen attachment to the silica surface. Our study provides valuable information on the dynamic film drainage process, which has crucial implications for many industrial applications involving high-viscosity oils.

Automated summary

In this study, the initial film drainage process between a high-viscosity bitumen droplet and a hydrophobic silica wafer was investigated. The results showed that the viscosity of the bitumen has a significant impact on the formation and drainage of the thin liquid film.