Understanding Molecular Interactions of Asphaltenes in Organic Solvents Using a Surface Force Apparatus

A surface force apparatus was used to study the intermolecular forces of asphaltenes in toluene and heptane. The repulsive interaction forces measured between two asphaltene surfaces in toluene were shown to have a steric nature and could be described by the Alexander-de Gennes theory on steric repulsion between two interacting polymer layers in good solvents at short separation distances under high compression forces. On the other hand, the adhesion forces measured between asphaltenes in heptane can be described by van der Waals forces, which are responsible for asphaltene aggregation and precipitation in paraffinic solvents. The asphaltene films adsorbed on mica were found to swell significantly in toluene but only moderately in heptane. In addition, an adhesion force was observed between an asphaltene surface and a mica surface in toluene. The results from this study provide an insight into the basic interaction mechanisms of asphaltenes in organic media and hence in crude oil and bitumen production.