(94f) "Multilayer'' Asphaltene Films at a Toluene/Water Interface

The Athabasca oil sands deposits in northern Alberta, Canada are a very important energy resource. Currently a warm water extraction process is used to extract bitumen from the oil sands ore. In order to prepare feed for upgrading, the extracted bitumen undergoes a froth treatment process where it is diluted with a solvent, centrifuged and mechanically separated in order to remove water and solids. The treated bitumen contains approximately 2-3% water and 0.5% solids and the remaining water is present in a stable water-in-oil emulsion form.

It is commonly believed that asphaltenes play an important role in emulsion stabilization by forming an interfacial film that covers the dispersed water droplets and prevents them from coalescing.

In this study, we study the behavior of asphaltene interfacial films at a toluene/water interface in order to understand their role in emulsion stabilization. A multilayer asphaltene film of about 3 ~ 4 layers thick was prepared by spreading an excess amount of asphaltene on a water subphase. Once toluene was placed on top of the multilayer film, some of the asphaltenes migrated to the bulk toluene topphase from the interface, leading to the formation of an asphaltene monolayer at the toluene/water interface. The presence of a monolayer film at the toluene/water interface was confirmed by Langmuir trough experiments, UV spectroscopic measurements of the collected topphase, and atomic force microscopy (AFM) imaging of the transferred Langmuir-Blodgett (LB) asphaltene films on silicon wafers.

This study shows that the Langmuir trough technique can be used directly to observe interfacial characteristics which otherwise can not be easily accessed by other techniques.