Influence of the Interactions of the Saturate, Aromatic, Resin, and Asphaltene Fractions on the Colloidal Structure of Asphalt: A Study Based on Molecular Simulation

Abstract

In the asphalt colloidal theory, the highest molecular weight asphaltene is located in the center of the micelle, and the lower molecular weight components (i.e., aromatics and saturates) are placed on the outside of the asphaltene aggregates. However, there is variability and uncertainty in the interpretation of the results of a large number of experiments that have directly and indirectly examined the structure of asphaltic colloids. The purpose of the study is to use quantum chemical calculations and molecular dynamics to examine the interactions (binding energy and interaction energy) of the saturate, aromatic, resin, and asphaltene (SARA) fractions in the formation of asphaltene micelles, and the spatial structure of the formations (distance and angle). According to our quantitative calculations, maltene (saturates, aromatics, and resins) molecules support the thermodynamic stability of asphaltene colloids. Saturates and aromatics play an identical role in maintaining the structural stability of asphalt colloids. Aging intensifies the accumulation of asphaltene dimers, and this accumulation is much less affected by maltene molecules than virgin asphalt. In addition, according to the results of molecular dynamics simulation, asphaltene micelles in sol asphalt are isolated from each other, and parallel asphaltene dimers are the main form of asphaltene dimers. There are interactions between asphaltene micelles in gel asphalt, and there are T-shape asphaltene dimers between the micelles. Aging results in an increase in the distance between asphaltene and resin as well as a decrease in the density of resin around the asphaltene, indicating that the resin is not able to strongly constrain the asphaltene aggregates to form an asphaltene-centered stable micelle core in gel asphalt. Herein, the interactions of the aforementioned four fractions in the formation of asphalt micelles and their spatial structures are methodically discussed from the perspective of molecular simulation. Compared with previous studies, we focused on researching the influences of saturates, aromatics, and resins on asphaltene and giving visualization and quantitative description of the spatial distribution characteristics of the four components that could reflect the colloidal structure.