Asphaltene Films at a Toluene/Water Interface

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 cannot be easily accessed by other techniques.