A multiscale method for simulating fluid interfaces covered with large molecules such as asphaltenes

Abstract

The interface between two liquids is fully described by the interfacial tension only for very pure liquids. In most cases the system also contains surfactant molecules which modify the interfacial tension according to their concentration at the interface. This has been widely studied over the years, and interesting phenomena arise, e.g. the Marangoni effect. An even more complicated situation arises for complex fluids like crude oil, where large molecules such as asphaltenes migrate to the interface and give rise to further phenomena not seen in surfactant-contaminated systems. An example of this is the "crumpling drop" experiments, where the interface of a drop being deflated becomes non-smooth at some point. In this paper we report on the development of a multiscale method for simulating such complex liquid-liquid systems. We consider simulations where water drops covered with asphaltenes are deflated, and reproduce the crumpling observed in experiments. The method on the nanoscale is based on using coarse-grained molecular dynamics simulations of the interface, with an accurate model for the asphaltene molecules. This enables the calculation of interfacial properties. These properties are then used in the macroscale simulation, which is performed with a two-phase incompressible flow solver using a novel hybrid level-set/ghost-fluid/immersed-boundary method for taking the complex interface behaviour into account. We validate both the nano-and macroscale methods. Results are presented from nano-and macroscale simulations which showcase some of the interesting behaviour caused by asphaltenes affecting the interface. The molecular simulations presented here are the first in the literature to obtain the correct interfacial orientation of asphaltenes. Results from the macroscale simulations present a new physical explanation of the crumpled drop phenomenon, while highlighting shortcomings in previous hypotheses.

Assessing the Interfacial Activity of Insoluble Asphaltene Layers: Interfacial Rheology versus Interfacial Tension

“…At higher concentrations, these aggregates form clusters, which have smaller binding energies than the ones occurring within the nanoaggregates. Molecular dynamics simulations (MD) and dissipative particle dynamics (DPD) are consistent with the presence of nanoaggregates, in bulk, − and at liquid/liquid interfaces. , …”

“…Molecular dynamics simulations (MD) and dissipative particle dynamics (DPD) are consistent with the presence of nanoaggregates, in bulk, 13−15 and at liquid/liquid interfaces. 16,17 Asphaltenes are typically one of the more polar fractions in crude oils and their chemical features, and possibly their colloidal nature (when present as nanoaggregates) make them prone to strongly adsorb at the oil/water interface due to the high capillary energy of colloidal nanoaggregates. 18 Asphaltene adsorption does, however, not only lead to a change in interfacial tension, but the formation of elastic skins around droplets has been reported.…”

Learning from reproducing computational results: introducing three principles and theReproduction Package

“…The authors did not report the amount of memory they used for their results. We also encountered this issue in another article we studied [ 12 ], and in previously mentioned prior work [ 86 , 87 ]. Guidance: G12.…”

Expanding the Applications of the SAFT-γ Mie Group-Contribution Equation of State: Prediction of Thermodynamic Properties and Phase Behavior of Mixtures

“…A heteronuclear model is implemented in SAFT-γ Mie, and a Mie (generalized Lennard-Jones) potential of variable repulsive and attractive ranges is used to represent the segment–segment group interactions. As evidenced by the growing number of published works − in which SAFT-γ Mie has been employed, the use of the approach is becoming widespread, not only in the traditional sense of GC modeling, but also as a basis for the development of coarse-grained force fields that are finding application in molecular simulations. − ,,,,,,,− ,,, …”