Molecular Orientation in Model Asphalts Using Molecular Simulation

Molecular simulations were used to analyze orientations of molecules within model asphalt mixtures. After choosing typical compounds to represent resin, maltene, and asphaltene components, molecular orientations and structures in two ternary asphalt mixtures were studied. The following conclusions are obtained from analyzing simulation results: (1) For nearest asphaltene molecules, orientations between neighboring molecules are affected by molecule structure and temperature. At high temperature, asphaltene molecules with long alkane branches prefer to pack almost parallel; at low temperatures, they prefer to pack almost perpendicular; at intermediate temperatures, they have a peak at around 40°. Highly aromatic asphaltene molecules prefer to stay almost parallel to each other at low temperatures and almost perpendicular at high temperatures. (2) Average orientation between neighboring molecules depends on distance between molecule centers of mass. Naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and 1,7-dimethylnaphthalene pack randomly over large center of mass distances, while at short distances, they pack almost parallel. (3) Deviations from planarity for the pure compounds naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and 1,7-dimethylnaphthalene are in the range of 0−20°, as are deviations for asphaltene molecules in ternary mixtures. The deviation increases for rings that include heteroatoms. (4) Different initial conditions indicate two alternatives for the presence and position of the first peak in the center of mass radial distribution function, while small distance intermolecular orientations remain almost the same.