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. 2020 Jun 30;25(13):3008.
doi: 10.3390/molecules25133008.

Emulsification of Surfactant on Oil Droplets by Molecular Dynamics Simulation

Yaoshuang Cheng  1 , Shiling Yuan  1
Affiliations

Emulsification of Surfactant on Oil Droplets by Molecular Dynamics Simulation

Yaoshuang Cheng et al. Molecules. .

Abstract

Heavy oil in crude oil flooding is extremely difficult to extract due to its high viscosity and poor fluidity. In this paper, molecular dynamics simulation was used to study the emulsification behavior of sodium dodecyl sulfonate (SDSn) micelles on heavy oil droplets composed of asphaltenes (ASP) at the molecular level. Some analyzed techniques were used including root mean square displacement, hydrophile-hydrophobic area of an oil droplet, potential of mean force, and the number of hydrogen bonds between oil droplet and water phase. The simulated results showed that the asphaltene with carboxylate groups significantly enhances the hydration layer on the surface of oil droplets, and SDSn molecules can change the strength of the hydration layer around the surface of the oil droplets. The water bridge structure between both polar heads of the surfactant was commonly formed around the hydration layer of the emulsified oil droplet. During the emulsification of heavy oil, the ratio of hydrophilic hydrophobic surface area around an oil droplet is essential. Molecular dynamics method can be considered as a helpful tool for experimental techniques at the molecular level.

Keywords: SDSn; asphaltene; emulsification; heavy oil; molecular dynamics.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
RMSD of oil droplets in water.
Figure 2
Figure 2
The configuration diagram at 50 ns in (a) system A (b) system B. SDSn are displayed in blue, yellow, and red spheres, ASP are displayed in rods and marked with rose red, and other heavy oil molecules are marked in gray. To be shown clearly, sodium ions and water molecules are removed.
Figure 3
Figure 3
The distance as a function of time between the centroid of the SDSn micelle and the centroid of the oil droplet in (a) (b) direction (x, y, z) (The blue area is the range of motion when they gather) (c) the straight-line distance.
Figure 4
Figure 4
The ratio of hydrophilic/hydrophobic area of SDSn and oil droplet in system A and the inset is the ratio from 0 to 5 ns.
Figure 5
Figure 5
The distribution of SDSn polar head coordinates over time. Oil droplets were represented with gray spheres, and 20 SDSn molecules are randomly selected from all SDSn.
Figure 6
Figure 6
Snapshots of system A without sodium ions and water at different time. (a) 0 ps, (b) 500 ps, (c) 1 ns, (d) 10 ns. SDSn were represented with the spherical drawing method, and heavy oil molecules were represented with bond drawing method, color identification: rose-red, asphaltene molecules, gray, other oil molecules.
Figure 7
Figure 7
Interaction energy of SDSn molecules with (a) SDSn and (b) ASP.
Figure 8
Figure 8
Partial amplification of hydrogen bond between SDSn and asphaltene at (a) 300 ps, (b) 400 ps, (c) 500 ps.
Figure 9
Figure 9
The PMF between the groups and the water molecule.
Figure 10
Figure 10
The number of H-bond as a function of time between the surface of oil droplet and water in system A.
Figure 11
Figure 11
Asphaltenes and Resins used in the simulation. System A contains anionic Asp 1 and 2, and system B contains Asp 1 and 2, respectively.
Figure 12
Figure 12
Simulation of the initial structure and dimensions. (a) Crude oil phase. (b) Heavy oil droplet. (c) Emulsified oil droplet. To be shown clearly, water molecules were removed in Figure (b) and (c).
Figure 13
Figure 13
Schematic diagram of SDSn emulsified oil droplets in system A and B.
See this image and copyright information in PMC

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