Simple Statistical Model for Branched Aggregates: Application to Cooee Bitumen

Lemarchand, Claire; Hansen, Jesper Schmidt

doi:10.1021/acs.jpcb.5b08320

Cited by 4 publications

(11 citation statements)

References 43 publications

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“…52 Lemarchand and Hansen employed molecular simulation and statistical mechanical and statistical models to study the aggregation within the "COOEE bitumen" system. 55, 56 A model based on the conditional probabilities for bond formation was shown to satisfactorily reproduce the size distribution of branched nanoaggregates observed in simulation, 55 and a master equation based on simple birth and death processes was found to provide a good description of the stability of linear asphaltene nanoaggregates and recapitulate the exponential nanoaggregate size distribution predicted by simulation. 56 A limited number of computational studies have investigated the molecular details of the assembly behavior of archipelago asphaltenes employing all-atom molecular models.…”

Section: Introductionmentioning

confidence: 78%

“…We also mapped out the temperature–pressure–toluene concentration phase diagram for assembly, employed nonlinear machine learning techniques to resolve pseudo-one-dimensional (1D) free energy landscapes, and showed toluene dispersant concentration to act as an effective temperature . Lemarchand and Hansen employed molecular simulation and statistical mechanical and statistical models to study the aggregation within the “COOEE bitumen” system. , A model based on the conditional probabilities for bond formation was shown to satisfactorily reproduce the size distribution of branched nanoaggregates observed in simulation, and a master equation based on simple birth and death processes was found to provide a good description of the stability of linear asphaltene nanoaggregates and recapitulate the exponential nanoaggregate size distribution predicted by simulation …”

Section: Introductionmentioning

confidence: 99%

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Coarse-Grained Molecular Simulation and Nonlinear Manifold Learning of Archipelago Asphaltene Aggregation and Folding

2018

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Asphaltenes constitute the heaviest aromatic component of crude oil. The myriad of asphaltene molecules falls largely into two conceptual classes: continental-possessing a single polyaromatic core-and archipelago-possessing multiple polyaromatic cores linked by alkyl chains. In this work, we study the influence of molecular architecture upon aggregation behavior and molecular folding of prototypical archipelago asphaltenes using coarse-grained molecular dynamics simulation and nonlinear manifold learning. The mechanistic details of aggregation depend sensitively on the molecular structure. Molecules possessing three polyaromatic cores show a higher aggregation propensity than those with two, and linear archipelago architectures more readily form a fractal network than ring topologies, although the resulting aggregates are more susceptible to disruption by chemical dispersants. The Yen-Mullins hierarchy of self-assembled aggregates is attenuated at high asphaltene mass fractions because of the dominance of promiscuous parallel stacking interactions within a percolating network rather than the formation of rodlike nanoaggregates and nanoaggregate clusters. The resulting spanning porous network possesses a fractal dimension of 1.0 on short length scales and 2.0 on long length scales regardless of the archipelago architecture. The incompatibility of the observed assembly behavior with the Yen-Mullins hierarchy lends support that high-molecular weight archipelago architectures do not occur at significant levels in natural crude oils. Low-dimensional free energy surfaces discovered by nonlinear dimensionality reduction reveal a rich diversity of metastable configurations and folding behavior reminiscent of protein folding and inform how intramolecular structures can be modulated by controlling asphaltene mass fraction and dispersant concentration.

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Section: Introductionmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Coarse-Grained Molecular Simulation and Nonlinear Manifold Learning of Archipelago Asphaltene Aggregation and Folding

2018

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“…Given the difficulties in experimentally characterizing asphaltenes, molecular simulations provide a powerful tool for studying their behavior. In particular, all-atom (AA) molecular dynamics simulations have examined the nanoaggregation of model asphaltenes in various solvents, at interfaces, and under various thermodynamic conditions. ,,− Unfortunately, the computational expense of atomically detailed simulations necessarily limits the duration, size, and scope of these studies, although recent computing advances with graphics processing units have somewhat extended these limits . Moreover, in the dilute conditions relevant for nanoaggregation, the vast majority of computational effort is expended in the simulating solvent.…”

Section: Introductionmentioning

confidence: 99%

Simple Simulation Model for Exploring the Effects of Solvent and Structure on Asphaltene Aggregation

2019

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Asphaltenes are operationally defined as the fraction of crude oil that is soluble in toluene but insoluble in n-heptane. According to the Yen−Mullins model, typical asphaltenes are relatively small molecules consisting of a single aromatic core flanked by aliphatic chains. The Yen−Mullins model posits that asphaltene aggregation proceeds via a hierarchical mechanism involving small nanoaggregates with stacked aromatic cores surrounded by a corona of aliphatic tails. In this work, we introduce a coarse-grained (CG) model for investigating the physical picture underlying the Yen− Mullins model and, more generally, the effects of the solvent character and molecular structure upon asphaltene selfassembly. By representing proposed asphaltenes in united atom detail, this CG model accurately describes their shape and conformational properties. Conversely, the CG model mimics varying solvent conditions by modulating the effective attraction between aliphatic and aromatic groups. Given the simplicity of this model, we performed long, replicate simulations of 147 different asphaltene solutions. As proposed by the Yen−Mullins model, island-type molecules readily form stacked aggregates under conditions that promote aromatic interactions. Interestingly, the onset of nanoaggregation appears to be insensitive to the aliphatic tails, although these tails may sterically stunt further growth of nanoaggregates. Consequently, nanoaggregates form more readily and grow larger under conditions that promote both aliphatic and aromatic interactions. In contrast, archipelago-type molecules also form large aggregates, but they do not demonstrate significant stacking interactions. Thus, the CG model reasonably describes the physical intuition of the Yen− Mullins picture and may prove to be useful for exploring later stages of asphaltene aggregation.

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“…The definition of the nanoaggregates in the case of Cooee bitumen is detailed in Refs. 27,28 It sums up to the following rule: two aromatic molecules are nearest neighbors in the same nanoaggregate if they are well aligned and close enough. More specifically, this rule is based on three thresholds.…”

Section: Bitumen Cohesion and Structurementioning

confidence: 99%

“…This fact has been reported and explained. 28 It is due to two competing effects when temperature increases: the first effect is the increase of thermal noise which tends to detach molecules from the nanoaggregates and decrease the nanoaggregate size; the second effect is the relative increase of the number of asphaltene molecules inside the nanoaggregates compared to other molecule types, which tends to increase the degree of branching of the aggregates and also their size. The non-monotonic behavior of the cohesive energy ce Ar between aromatic molecules is due to the same cause.…”

Section: Bitumen Cohesion and Structurementioning

confidence: 99%

Dynamics and Structure of Bitumen–Water Mixtures

2016

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Systems of Cooee bitumen and water up to 4% mass are studied by molecular dynamics simulations. The cohesive energy density of the system is shown to decrease with an increasing water content. This decrease is due mainly to an increase in the interaction energy which is not high enough to counterbalance the increase in volume due to the addition of water. It is not due to a decrease of interaction energy between the slightly polar asphaltene molecules. The water molecules tend to form a droplet in bitumen. The size and the distribution of sizes of the droplets are quantified, with multiple droplets being more stable at the highest temperature simulated. The droplet is mainly located close to the saturates molecules in bitumen. Finally, it is shown that the water dynamics is much slower in bitumen than in pure water because it is governed by the diffusion of the droplet and not of the single molecules.

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Simple Statistical Model for Branched Aggregates: Application to Cooee Bitumen

Cited by 4 publications

References 43 publications

Coarse-Grained Molecular Simulation and Nonlinear Manifold Learning of Archipelago Asphaltene Aggregation and Folding

Coarse-Grained Molecular Simulation and Nonlinear Manifold Learning of Archipelago Asphaltene Aggregation and Folding

Simple Simulation Model for Exploring the Effects of Solvent and Structure on Asphaltene Aggregation

Dynamics and Structure of Bitumen–Water Mixtures

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