Mesoscopic Simulation of Aggregate Characteristics of Asphaltene Molecules Under Shear Fields

Behaviors of asphaltene molecules in toluene under a shear force field were investigated by dissipative particle dynamics (DPD). The results showed that asphaltene molecules aggregated into nanoaggregates (NAs) in three forms, mainly in the face-to-face type, which contained up to 7 asphaltene molecules. In the aggregates, the distance between aromatic sheets (ASes) of adjacent asphaltene molecules was about 6 Å, and the minimum was 5.49 Å. The composition of NAs changed dynamically. In the absence of shear, the aggregates lasted for more than 3000 ps and up to 8000 ps. The asphaltene molecules in an aggregate might reaggregate once dispersed. Both the number and size of the aggregates decreased under the shear force field, and the duration decreased to less than 1000 ps. The direction of the ASes was distributed randomly when the shear rate was zero. Once sheared, the angle between the ASes and the shear force field plane decreased while the range of it expanded. The ASes tended to be parallel to the shear field and the angle between the two concentrated below 40°. As the shear rate increased, the angle decreased and the distribution was more concentrated.