Molecular dynamics (MD) simulations were used to study the aggregation of model molecules representing some structural features of asphaltenes in different solvents, namely, water, toluene, and heptane. Three different model molecules with similar molecular weights were developed as representatives of continental- and archipelago-type structures of asphaltenes. Two types of continental models were employed, one containing no charged entities and another containing one anionic terminal carboxylic group on an aliphatic chain. Analysis of the aggregate structures in single pure solvents indicate stacking of the polyaromatic rings as the dominant structural feature of the aggregates. Simulations were then conducted to study aggregation and partitioning of these model molecules in binary mixtures of water and toluene. A key observation from these simulations was that uncharged molecules did not congregate at the toluene−water interface, whereas charged terminal groups had a distinct affinity for the toluene−water interface. In the presence of charged entities, the resulting aggregate had a complex three-dimensional structure containing stacked polyaromatic rings tethered to the interface by the anionic terminal groups.

Molecular dynamics (MD) simulations were used to study the nanoaggregation of model asphaltene molecules in binary mixtures of toluene and water. Four types of model asphaltenes were studied: continental (C), Violanthrone-79 (VO-79), anionic continental (AC), and thiophenic anionic continental (TAC). Of these, the first two were uncharged, whereas the AC and TAC contained a side chain with a carboxylic terminal group. In all simulations, the model asphaltenes partitioned completely into the toluene phase of the phase-separated solvent mixture. The asphaltene molecules containing charged terminal groups remained tethered to the toluene-water interface (interface-bound), whereas uncharged asphaltenes aggregated within the central region of the toluene layer (core-bound). The stacked polyaromatic rings of the asphaltene aggregates showed a distinct preference to incline almost perpendicular to the toluene-water interface. Analysis of the mean square displacements of the asphaltenes reveals that for both charged and uncharged model asphaltenes, the lateral diffusion parallel to the toluene-water interface is dominant, whereas the transverse diffusion (normal to the interface) becomes significantly suppressed. This observation suggests that in thin films of toluene trapped between two aqueous phases, both interface-bound and core-bound asphaltenes, although subjected to vastly different interaction scenarios, exhibit similar diffusion behavior.

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The interaction of xenon with silver ETS-10 is found to be unusually strong. Xenon adsorption was studied on Na-ETS-10 and its silver exchanged counterpart, Ag-ETS-10, by gas chromatography and gravimetric adsorption. High adsorption capacities were observed even at low pressure (6 wt % Xe at 0.5 Torr and 25 °C). High isosteric heats of adsorption for xenon on Ag-ETS-10 were observed, higher than on any other adsorbent reported to date. High selectivity of xenon over nitrogen and oxygen is also observed, especially at low xenon partial pressures. The great affinity of this adsorbent for xenon is attributed to the presence of silver nanoparticles, which grow on the surface of the molecular sieve after heat treatment of Ag exchanged material.

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