Molecular dynamics study of “quasi-gemini” surfactant at n-decane/water interface: The synergistic effect of hydrophilic headgroups and hydrophobic tails of surfactants on the interface properties

In response to the problem of complex interaction between oil and water in the oil−water interface, especially heavy oil and water, this study investigated the effects of complex surfactants on the interaction of two phases and their aggregation characteristics by molecular dynamics simulation. The results showed that increasing the content of sodium lauryl polyether carboxylate (AEC-9Na) was beneficial to the coordination between it and alkyl glycoside (APG-10), improved the interfacial activity, and enhanced the interfacial stability of the composite system, and the best effect was achieved when AEC-9Na:APG-10 = 8:2. The thickness of the oil and water film on the oil−water interface was irregular. When the concentration of AEC-9Na was lower than that of APG-10, the total thickness of the interfacial film (t total ) first increased. When the content of AEC-9Na is higher, a large number of sodium ions were adsorbed near the −COO − group of AEC-9Na, which will polarize out of the hydration layer structure and attract water molecules from the second hydration layer on the heavy oil surface to the first hydration layer through electrostatic interaction. Then, the thickness of the interface film was compressed, and the interface film was reduced. When the ratio increased to 10:0, the oil and water phase competed to adsorb surfactant molecules, and the headgroup tended to lay on the interface. Moreover, the hydrophilicity of the surfactant layer was weakened, and the thickness of the water film decreased. The distribution of surfactant was looser than 8:2, the light components of heavy oil molecules (saturated and aromatic hydrocarbons) entered the gap between surfactants in large quantities, and the hydrophobic tail chain tended to be laid on the oil−water interface. The oleophilicity of the surfactant layer increased, and the thickness of the oil film remarkably increased, so the total thickness of the interface film increased again.

Section: Results and Analysismentioning

confidence: 99%

Molecular Dynamics Simulation of the Effects of Complex Surfactants on Oil–Water Interaction and Aggregation Characteristics at the Interface

Xian,

Ye,

Tang

et al. 2023

“…A value of less than 0 is indicative of a high absolute value, which indicates that the IFE is strong and corresponds to the formation of a stable interface. Its specific value can be calculated by using Formula . , I F E = E t o t a l − ( n E surfactant , s i n g l e + E o i l − w a t e r ) n where E total is the total energy of the modeled liquid film system, E surfactant,single denotes the energy of a single DOAPA@NaSal-H + , E oil–water represents the total energy of the modeled liquid film system without the presence of the surfactant, and n represents the number of surfactants.…”

Section: Methodsmentioning

confidence: 99%

Investigation of the Stability Mechanism of Stimulus-Responsive Wormlike Micelle-CO₂ Foams in the Oil Phase

He,

Zheng,

Lin

et al. 2024

Foam flooding is an important tool for reservoir development. This study aims to further investigate the interaction between stimulus-responsive wormlike micelle (WLM)-CO2 foams and crude oil. We performed micromorphology experiments as our major studies and used molecular dynamics simulations as an auxiliary tool for interfacial analysis. We utilized foam generation, liquid separation, and defoaming as the entry points of experimental research and energy as the quantitative assessment index to investigate the dynamic process of the action of different oil contents and oil phase types in a DOAPA@NaSal-H+ foam system. We also examined the role of NaSal in the generation and development of the foam system. Results indicated that the law of crude oil’s effect on foam could be summarized as “low contents are beneficial and high contents are harmful.” In addition, although the DOAPA@NaSal-H+ foam system has high compatibility for saturated and aromatic hydrocarbons, it is highly suitable for application in reservoir environments with relatively high asphaltene and resin contents. Through combined experimental and simulation approaches, we clarified the law governing the stability of the DOAPA@NaSal-H+ foam system in different oil-containing environments, identified the key role of NaSal, and provided a reference for the targeted application of the DOAPA@NaSal-H+ foam system in different oil reservoirs.

“…Nevertheless, in MD studies of surfactants, it has always been difficult to compare the interface properties of different newly designed surfactants at CMC. [26][27][28][29]31 Previous MD studies often used models with fixed Γ, and some did not clarify whether Γ was fixed. As a result, it is impossible to screen surfactants with better performance directly and accurately.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Most experimental studies on the interfacial properties of surfactants are conducted at or above the critical micelle concentration (CMC), which is when the surface or interface excess concentration (Γ) reaches its maximum value, Γ max . Nevertheless, in MD studies of surfactants, it has always been difficult to compare the interface properties of different newly designed surfactants at CMC. − , Previous MD studies often used models with fixed Γ, and some did not clarify whether Γ was fixed. As a result, it is impossible to screen surfactants with better performance directly and accurately.…”

Section: Introductionmentioning

confidence: 99%

Mechanism Analysis and Property Prediction of Extended Surfactants Based on the Respectively Optimized Force Field

Yu,

Gao,

Ding

et al. 2023

Self Cite

Extended surfactants represent a novel class of anionic–nonionic surfactants with exceptional performance and unique application value in chemically enhanced oil recovery. Although molecular dynamics (MD) simulations can efficiently screen these surfactants, the current research is limited. Here, it is proven for the first time that existing generic force fields (GAFF and CHARMM) cannot accurately describe extended surfactants, and traditional approaches are insufficient for obtaining precise charge parameters. The concept of the respectively optimized force field (ROFF) with the purports of specialization and accuracy is proposed to construct high-accuracy models for MD simulations, and a new approach is developed to simulate the interface model. By combining the newly specialized alkane model, ROFF-based surfactant models, and the innovative simulation protocol, high accuracy and reliability can be obtained in predicting hydration free energies, minimum of area per molecule, and critical micelle concentration of extended surfactants. Key properties of the newly designed extended surfactants in conventional oil–water interfaces and oil reservoir environments are comprehensively predicted by using advanced analytical and characterization methods. Furthermore, the more rigorous mechanism underlying the special amphiphilicity of the extended surfactant is revealed, potentially offering significant improvements over previous empirical perspectives.