Solvent-Regulated Free-Energy Landscapes Govern Asphaltene Aggregation Pathways

Abstract

Asphaltene aggregation governs many flow-assurance challenges in petroleum systems, yet the microscopic role of the solvent environment in controlling aggregation pathways remains incompletely understood. Here, we combine all atom molecular dynamics simulations with a minimal statistical aggregation framework to investigate how aromatic and aliphatic solvents reshape asphaltene assembly from dimerization to mesoscale cluster formation. Although both toluene and heptane exhibit strong local aromatic stacking, the simulations reveal fundamentally different aggregation pathways driven by solvent-mediated interfacial effects. In toluene, aromatic solvation stabilizes exposed asphaltene cores and frustrates persistent growth, leading to small, open, weakly connected nanoaggregates. In contrast, heptane promotes aggregation through larger solvent-coordination loss, broader configurational accessibility, and progressive compactification toward nearly space-filling clusters. By quantitatively linking solvent coordination, solvent-contact free energies, aggregate morphology, and cluster statistics within a unified framework, we show that solvent quality controls aggregation not only through solubility, but by reshaping the underlying aggregation free-energy landscape. The resulting framework provides a molecular interpretation of solvent-dependent aggregation and offers routes for controlling asphaltene association through solvent environment or additive design.