(342c) Aging Oil-Water Interfaces with Asphaltene Adsorption: Interface Rheology and Heterogeneity

Water is often used in the production and processing of oil, but the water and oil must ultimately be separated. Such separations can be very challenging, because various surface-active materials naturally exist in crude oil that stabilize water-oil interfaces.

Polycyclic aromatic hydrocarbons called asphaltenes are a broad class of surface-active compounds that adsorb at water-oil interfaces and stabilize such emulsions. To facilitate the separation of oil and water, chemical additives like ethylcellulose (EC) are often introduced to destabilize the emulsion. However, the mechanism needs to be investigated to guide the development of the additives.

We use ferromagnetic microbuttons as interfacial rheological probes to study the evolution of oil/water interfaces as asphaltenes adsorb, and the effect of EC on the evolution of the mechanical properties of the interface. Oil/water interfaces progressively stiffen as asphaltenes adsorb; this process, however, can be prevented or reversed with the addition of EC.

To probe the mechanism behind these observations, we visualize the deformation (strain) field of the oil/water interface in response to the stresses imposed by the microbutton. Asphaltene-adsorbed oil/water interfaces show significant mechanical heterogeneity, with pronounced stiff and weak regions. EC affects these heterogeneous regions differently, suggesting various hypotheses for its action on asphaltene-stabilized interfaces.

Our study reveals the rich properties of water/asphaltene/oil interfaces, and highlights new tools to probe mechanically heterogeneous interfaces as they evolve in response to their local chemical environments.