On Mimicking Nano-particulate Behaviors of Asphaltenes in Solution and at Interfaces

Abstract

The nature and structure of asphaltene nanoaggregates are frequently the subject of debate and speculation in the literature. The continental asphaltene nano-aggregate model, characterized by the presence of alkyl chains on their surface, and the archipelago nano-aggregate model, characterized by a diverse mix of functionalities on their outer surfaces, co-exist. In this work, these two prototypical asphaltene nanoaggregate models are probed using neutral gold-core nanoparticles with alkyl, aromatic, and alkanol functionalities on their surfaces. The nanoparticles are synthesized and characterized as part of this work. Their enthalpies of solution, and interfacial tensions reflect interactions between the organic ligands on their surface and the surrounding media. The measured values are compared with the corresponding values for Athabasca pentane asphaltenes. The solution calorimetry of asphaltenes is qualitatively represented by the gold-alkyl nanoparticles. The interfacial tension values are qualitatively represented by the gold-aromatic nanoparticles. Quantitative comparisons are precluded because the number and nature of interaction sites on asphaltene aggregates, and the possible impact of asphaltene aggregate solubility on measurements are unknown. From this preliminary exploratory study, it is clear that to mimic the behaviors of asphaltenes in solution and at interfaces, a mix of ligands on nanoparticle surfaces is required with alkyl ligands playing a primary role, and aromatic ligands playing a secondary role. N-alkanol ligands do not appear to play a significant role. The outcomes of this work support both the continental and archipelago asphaltene nanoaggregate models, and a number of lines of inquiry for future work are suggested. For example, it is not clear whether the best gold-ligand mimics for asphaltenes comprise mixes of particles with different ligands or individual particles with multiple ligands, and other ligand types remain to be explored. Nanopaticle synthesis will pose significant challenges for these future works.