Regulation of Interfacial Adsorption Conformation and Aggregation Morphology on the Desorption of Asphaltene from the Oil-Water Interface.

The stability of the emulsification system plays an important role in crude oil extraction and processing. The adsorption conformation and aggregation morphology of asphaltenes at the interface are the key factors determining emulsion stability. Here, we combine molecular dynamics simulation and the umbrella sampling method to systematically investigate the desorption free energy of asphaltene molecules from the oil-water interfaces under the conditions of three common ions (Na+, Ca2+, Mg2+) and different concentrations of asphaltene, quantifying and evaluating the interfacial adsorption stability of asphaltene by analyzing its adsorption conformation and aggregation morphology. We find that the adsorption conformation and aggregation morphology of asphaltenes have a significant impact on their desorption free energy. As the asphaltene concentration increases, the tightness of asphaltene aggregates increases, and a dominant adsorption conformation emerges. The tilt angle of this dominant conformation increases with the increase in concentration, enhancing the van der Waals interactions and thereby enlarging the desorption resistance. In contrast, the addition of Na+, Ca2+, or Mg2+ promotes the interaction between asphaltene and the interface but disrupts the orderliness of the adsorption conformation of asphaltenes. This results in a looser interfacial cluster structure of the asphaltene with weakened interactions between molecules. Eventually, the desorption free energy of asphaltene decreases, making the desorption process easier. This study clarifies that the adsorption conformation and aggregation morphology are the key factors regulating the dynamic adsorption/desorption behaviors of asphaltenes at the interfaces, providing a theoretical basis for revealing and regulating the behavior of asphaltenes at the oil-water interfaces.