title: Mesoscale Simulation of Asphaltene Aggregation.
abstract: Asphaltenes constitute a heavy aromatic crude oil fraction with a propensity to aggregate and precipitate out of solution during petroleum processing. Aggregation is thought to proceed according to the Yen-Mullins hierarchy, but the molecular mechanisms underlying mesoscopic assembly remain poorly understood. By combining coarse-grained molecular models parametrized using all-atom data with high-performance GPU hardware, we have performed molecular dynamics simulations of the aggregation of hundreds of asphaltenes over microsecond time scales. Our simulations reveal a hierarchical self-assembly mechanism consistent with the Yen-Mullins model, but the details are sensitive and depend on asphaltene chemistry and environment. At low concentrations asphaltenes exist predominantly as dispersed monomers. Upon increasing concentration, we first observe parallel stacking into 1D rod-like nanoaggregates, followed by the formation of clusters of nanoaggregates associated by offset, T-shaped, and edge-edge stacking. Asphaltenes possessing long aliphatic side chains cannot form nanoaggregate clusters due to steric repulsions between their aliphatic coronae. At very high concentrations, we observe a porous percolating network of rod-like nanoaggregates suspended in a sea of interpenetrating aliphatic side chains with a fractal dimension of ∼2. The lifetime of the rod-like aggregates is described by an exponential distribution reflecting a dynamic equilibrium between coagulation and fragmentation.
authors.affiliation: Department of Physics, ‡Department of Materials Science and Engineering, and ¶Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Jiang
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Physics, ‡Department of Materials Science and Engineering, and ¶Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Ferguson