Molecular Dynamics Simulations of the Oil-Detachment from the Hydroxylated Silica Surface: Effects of Surfactants, Electrostatic Interactions, and Water Flows on the Water Molecular Channel Formation

Abstract

The detachment process of an oil molecular layer situated above a horizontal substrate was often described by a three-stage process. In this mechanism, the penetration and diffusion of water molecules between the oil phase and the substrate was proposed to be a crucial step to aid in removal of oil layer/drops from substrate. In this work, the detachment process of a two-dimensional alkane molecule layer from a silica surface in aqueous surfactant solutions is studied by means of molecular dynamics (MD) simulations. By tuning the polarity of model silica surfaces, as well as considering the different types of surfactant molecules and the water flow effects, more details about the formation of water molecular channel and the expansion processes are elucidated. It is found that for both ionic and nonionic type surfactant solutions, the perturbation of surfactant molecules on the two-dimensional oil molecule layer facilitates the injection and diffusion of water molecules between the oil layer and silica substrate. However, the water channel formation and expansion speed is strongly affected by the substrate polarity and properties of surfactant molecules. First, only for the silica surface with relative stronger polarity, the formation of water molecular channel is observed. Second, the expansion speed of the water molecular channel upon the ionic surfactant (dodecyl trimethylammonium bromide, DTAB and sodium dodecyl benzenesulfonate, SDBS) flooding is more rapidly than the nonionic surfactant system (octylphenol polyoxyethylene(10) ether, OP-10). Third, the water flow speed may also affect the injection and diffusion of water molecules. These simulation results indicate that the water molecular channel formation process is affected by multiple factors. The synergistic effects of perturbation of surfactant molecules and the electrostatic interactions between silica substrate and water molecules are two key factors aiding in the injection and diffusion of water molecules and helpful for the oil detachment from silica substrate.

Insight into the pressure-induced displacement mechanism for selecting efficient nanofluids in various capillaries

“…Among others, adding extra chemicals (surfactant, polymer) can effectively adjust the property of injecting fluids, and meanwhile change the composition of capillary surface with their adsorption, which is thus efficient in regulating two-phase displacement process. 14,15 Currently, the development of new chemical fluids to regulate two-phase displacement involves a major challenge, as many studies observed that the efficiency of chemical fluid is capillary dependent. For example, according to the worldwide enhanced oil recovery (EOR) survey, not all the reservoirs can adopt same chemical fluids, and the performance of a specific chemical fluid varies significantly in different capillaries.…”

Effects of Surfactant Charge and Molecular Structure on Wettability Alteration of Calcite: Insights from Molecular Dynamics Simulations

“…The utility of MD simulations for petroleum engineering is well recognized and numerous studies have been reported concerning the properties of oil–water and oil–mineral interfaces, − including surfactants. ,, There are comparatively fewer reports specifically focused on the wettability alteration of initially oil-wet surfaces by surfactants, − which, moreover, rely on models that seem to largely disregard the experimentally well-documented and generally accepted properties of the minerals, the oil, as well as the mechanisms of the interaction between the two. In particular, rather than using the most naturally abundant {1,0,1̅,4} calcite surface , to model the carbonate substrate, a different and apparently arbitrary {1,0,0} plane is used.…”

Evidence for water ridges at oil–water interfaces: implications for ion transport

“…52 The transport of ions across the interface is usually initiated by compounds such as surfactants and lipophilic complexes, inducing the formation of specific interfacial structures, for instance a water channel. 51,53,54 These specific interfacial structures bring a challenge for the free energy calculation. Recently, combined with MD simulations, some enhanced sampling methods such as replica exchange, 55 accelerated molecular dynamics, 56 umbrella sampling, 57 and metadynamics 58 have been proposed and developed to obtain a more accurate description of the free energy during ion transfer across interfaces.…”