  Understanding of the molecular interaction between asphaltenes and other
molecules, which may act as its solvents, provides insights into the nature of
its stability in petroleum fluids and its phase transitions. Molecular dynamics
simulations were performed and reported here on systems consisting of a single
asphaltene molecule and pure solvents. Three types of asphaltenes with
different architectures, molecular weights, and heteroatoms content were
investigated. Water and ortho-xylene were selected to be the interacting
solvents. All simulations were performed by using GROMACS software. OPLS_AA
potential model for hydrocarbons and SPC/E potential model for water were used
in simulations. It was shown that the polar functional groups in asphaltenes
were responsible for generating hydrogen bonds (HBs) between asphaltenes and
water. It was also demonstrated that both electrostatic (ES) and van der Waals
(vdW) interaction energies between asphaltenes and water had important roles.
On the contrary, ES between asphaltenes and ortho-xylene had a minor effect as
compared with the vdW. In all cases, potential energies increased rather
slightly when the pressure was boosted. Moreover, they decreased noticeably
when the temperature was raised. HBs between asphaltenes and water were not
influenced by pressure change. Additionally, they increased slightly when the
temperature was dropped.
