Gold Core Nanoparticle Mimics for Asphaltene Behaviors in Solution and at Interfaces

摘要

Asphaltenes are a poorly defined class of self-assembling and surface active molecules present in crude oils. The nature and structure of the nanoaggregates they form remain subjects of debate and speculation. In this exploratory work, the surface properties of asphaltene nanoaggregates are probed using electrically neutral 5 nm diameter gold-core nanoparticles with alkyl, aromatic, and alkanol functionalities on their surfaces. These custom synthesized nanoparticles are characterized, and their enthalpies of solution at near infinite dilution and the interfacial tensions of solutions containing these nanoparticles are compared with the corresponding values for Athabasca pentane asphaltenes. The enthalpies of solution of these asphaltenes in toluene, heptane, pyridine, ethanol, and water are consistent with the behavior of gold-alkyl nanoparticles. The interfacial tension values of these asphaltenes at toluene water and (toluene + heptane) water interfaces are consistent with the behavior of gold biphenyl nanoparticles as are the tendencies for these asphaltenes and gold-biphenyl nanoparticles to "precipitate" in toluene + heptane mixtures. Gold-alkyl nanoparticles are minimally surface active at toluene water and (toluene + heptane) water interfaces and remain dispersed in all toluene + heptane mixtures. The behavior of these asphaltenes in solution and at interfaces is inconsistent with the behavior of gold-n-alkanol nanoparticles. The outcomes of this formative work indicate potential roles for aromatic submolecular motifs on aggregate surfaces as a basis for interpreting asphaltene nanoparticle flocculation and interfacial properties, while alkyl submolecular motifs on aggregate surfaces appear to provide a basis for interpreting other aspects of asphaltene solution behavior. A number of lines of inquiry for future work are suggested.