Asphaltene aggregation studied by molecular dynamics simulations: role of the molecular architecture and solvents on the supramolecular or colloidal behavior

Abstract

Asphaltene aggregation is a subject under vivid discussion: There are several parameters one needs to determine before its behavior can be mastered and better target solutions can be tailored. The nature of asphaltene aggregation (colloidal or supramolecular) and the role of solvents and their mixtures are among the least understood parameters in asphaltene science. This paper addresses molecular dynamic simulations to correlate the aggregation properties of asphaltenes, their molecular structure and the concentration of these solvents. We show that the formation of the nanoaggregate depends, primarily, on the size of the conjugated core and on the eventual presence of polar groups capable of forming H-bonds. Heteroatoms on the conjugated core do not change their shape or type of aggregation but may induce stronger π - π interactions. The macroaggregation formation depends upon the length of the lateral chains of asphaltenes and also on the presence of polar groups at its end. Moreover, n-heptane and water may interact selectively with asphaltenes in function of their molecular architecture. Given this fact and the aggregation behavior observed, we advocate toward the assumption that a colloidal behavior of asphaltenes might be a particular case of a more general model, based on a supramolecular description.