Molecular dynamics simulations of AOT at isooctane/water interface

Comprehensive review of the interfacial behavior of water/oil/surfactant systems using dissipative particle dynamics simulation

A comprehensive understanding of interfacial behavior in water/oil/surfactant systems is critical to evaluating the performance of emulsions in various industries, specifically in the oil and gas industry. To gain fundamental knowledge regarding this interfacial behavior, atomistic methods, e.g., molecular dynamics (MD) simulation, can be employed; however, MD simulation cannot handle phenomena that require more than a million atoms. The coarse-grained mesoscale methods were introduced to resolve this issue. One of the most effective mesoscale coarse-grained approaches for simulating colloidal systems is dissipative particle dynamics (DPD), which bridges the gap between macroscopic time and length scales and molecular-scale simulation. This work reviews the fundamentals of DPD simulation and its progress on colloids and interface systems, especially surfactant/water/oil mixtures. The effects of temperature, salt content, a water/oil ratio, a shear rate, and a type of surfactant on the interfacial behavior in water/oil/surfactant systems using DPD simulation are evaluated. In addition, the obtained results are also investigated through the lens of the chemistry of surfactants and emulsions. The outcome of this comprehensive review demonstrates the importance of DPD simulation in various processes with a focus on the colloidal and interfacial behavior of surfactants at water-oil interfaces.

Dynamic performance of duolayers at the air/water interface. 2. Mechanistic insights from all-atom simulations

The novel duolayer system, comprising a monolayer of ethylene glycol monooctadecyl ether (C18E1) and the water-soluble polymer poly(vinylpyrrolidone) (PVP), has been shown to resist forces such as wind stress to a greater degree than the C18E1 monolayer alone. This paper reports all-atom molecular dynamics simulations comparing the monolayer (C18E1 alone) and duolayer systems under an applied force parallel to the air/water interface. The simulations show that, due to the presence of PVP at the interface, the duolayer film exhibits an increase in chain tilt, ordering, and density, as well as a lower lateral velocity compared to the monolayer. These results provide a molecular rationale for the improved performance of the duolayer system under wind conditions, as well as an atomic-level explanation for the observed efficacy of the duolayer system as an evaporation suppressant, which may serve as a useful guide for future development for thin films where resistance to external perturbation is desirable.

Molecular mechanism of stabilization of thin films for improved water evaporation protection

All-atom molecular dynamics simulations and experimental characterization have been used to examine the structure and dynamics of novel evaporation-suppressing films where the addition of a water-soluble polymer to an ethylene glycol monooctadecyl ether monolayer leads to improved water evaporation resistance. Simulations and Langmuir trough experiments demonstrate the surface activity of poly(vinyl pyrrolidone) (PVP). Subsequent MD simulations performed on the thin films supported by the PVP sublayer show that, at low surface pressures, the polymer tends to concentrate at the film/water interface. The simulated atomic concentration profiles, hydrogen bonding patterns, and mobility analyses of the water-polymer-monolayer interfaces reveal that the presence of PVP increases the atomic density near the monolayer film, improves the film stability, and reduces the mobility of interfacial waters. These observations explain the molecular basis of the improved efficacy of these monolayer/polymer systems for evaporation protection of water and can be used to guide future development of organic thin films for other applications.

Molecular dynamics study of alkyl benzene sulfonate at air/water interface: effect of inorganic salts

Molecular dynamics simulations have been performed to investigate the effect of inorganic salts on the structural and dynamic properties of alkyl benzene sulfonate monolayer formed at the air/water interface. The alkyl benzene sulfonates are two surfactant isomers in the family of sodium hexadecane benzene sulfonates defined by 1C16 and 5C16, indicating a benzene sulfonate group attached to the first and fifth carbon atom in hexadecane backbone. It has been observed that both benzene ring groups and headgroups (-SO(3)(-)) are hydrated due to their polar nature. Water molecules can form stable hydrogen bonds with headgroups of surfactants, and the counterions (Na(+), Mg(2+), or Ca(2+)) are distributed close to the air/water interface. The stronger electrostatic repulsion drives the 1C16 monolayer arranged in disorder in comparison with 5C16, and the presence of inorganic salts may screen electrostatic repulsions between headgroups and decrease the thickness of the interfacial water layer, which follows the series Ca(2+) > Mg(2+) > Na(+). The order of inorganic salt tolerance of two surfactants is 5C16 > 1C16. The counterions may penetrate into the hydration shell of the surfactant headgroups and restrict the mobility of the water molecules situated in this area.