Interaction energy in Maya-oil asphaltenes: A molecular mechanics study

The interaction energy in vacuum between large-scale (630 atom) Maya-oil as phaltenes and that for an asphaltene-resin dimer has been calculated using molecular mechanics for various relative orientations and distances, keepin g a frozen-structure scheme. In the case of asphaltene-asphaltene interacti ons, it is found that the anti-aliphatic conformation (i.e., with the monom er alkyl branches far away from each other) with parallel well-defined arom atic regions constitutes the most stable structure for an asphaltene dimer. For the asphaltene-resin case, a set of stable configurations is found mai nly associated with the exposed asphaltene aromatic regions. In this paper, a survey of the interaction energy for a particular asphaltene-resin confi guration is reported and corn pared with the asphaltene-asphaltene case. Th e interaction energies as a function of relative distance are parameterized through an analytical expression distinguishing among Coulomb, dispersion, and London contributions. Finally, an effective-medium approach to estimat e the effect of the embedding medium on the interaction energy is proposed through a dielectric scaling of the Coulomb and London contributions.