Interfacial assignment of branched-alkyl benzene sulfonates: A molecular simulation

Liu, Zi Yu; Wei, Ning; He, Zhiming; Zhang, Lei; Liao, Qi; Zhang, Lu

doi:10.1063/1.4935339

Cited by 17 publications

(4 citation statements)

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“…The present work is limited to the investigation of vapour-liquid interfaces of binary mixtures of molecular fluids. Related work on electrolyte solutions and ionic liquids [2,[37][38][39][40][41][42][43], on the behaviour of surfactants at interfaces [44][45][46][47][48][49], as well as on the enrichment of components at liquid-liquid interfaces [27,31,33,[50][51][52][53][54] is not covered. Since theoretical methods for the prediction of component density profiles, namely molecular simulation, DGT, and DFT have been reviewed in detail elsewhere [55][56][57][58][59] their description is not subject of the present paper.…”

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confidence: 99%

Enrichment at vapour–liquid interfaces of mixtures: establishing a link between nanoscopic and macroscopic properties

Stephan

Hasse

2020

International Reviews in Physical Chemistry

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Component density profiles at vapour-liquid interfaces of mixtures can exhibit a non-monotonic behaviour with a maximum that can be many times larger than the densities in the bulk phases. This is called enrichment and is usually only observed for low-boiling components. The enrichment is a nanoscopic property which can presently not be measured experimentally -in contrast to the classical Gibbs adsorption. The available information on the enrichment stems from molecular simulations, density gradient theory, or density functional theory. The enrichment is highly interesting as it is suspected to influence the mass transfer across interfaces. In the present work, we review the literature data and the existing knowledge on this phenomenon and propose an empirical model to establish a link between the nanoscopic enrichment and macroscopic properties -namely vapour-liquid equilibrium data. The model parameters were determined from a fit to a dataset on the enrichment in about 100 binary Lennard-Jones model mixtures that exhibit different types of phase behaviour, which has recently become available. The model is then tested on the entire set of enrichment data that is available in the literature, which includes also mixtures containing nonspherical, polar, and H-bonding components. The model predicts the enrichment data from the literature (2,000 data points) with an AAD of about 16%, which is below the uncertainty of the enrichment data. This establishes a direct link between measurable macroscopic properties and the nanoscopic enrichment and enables predictions of the enrichment at vapour-liquid interfaces from macroscopic data alone.

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confidence: 99%

Enrichment at vapour–liquid interfaces of mixtures: establishing a link between nanoscopic and macroscopic properties

Stephan

Hasse

2020

International Reviews in Physical Chemistry

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“…12 a)). In particular, MD simulations are frequently used for the prediction of thermophysical bulk properties of lubricants [115,206,240,255,322], but can also be used for homogeneous solid phases. Simulations of lubricants usually aim at predicting transport properties, in particular the viscosity, as well as the heat conductivity, the density, the heat capacity, and the compressibility at a given pressure and temperature.…”

Section: Computational Tribology On the Atomistic Levelmentioning

confidence: 99%

Influence of Lubrication on Tribological Nanoscopic Contact Processes

Stephan

2024

Preprint

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Lubricated tribological contact processes are important in both nature and in many technical applications. Fluid lubricants play an important role in contact processes, e.g. they reduce friction and cool the contact zone. The fundamentals of lubricated contact processes on the atomistic scale are, however, today not fully understood. A lubricated contact process is defined here as a process, where two solid bodies that are in close proximity and eventually in parts in direct contact, carry out a relative motion, whereat the remaining volume is submersed by a fluid lubricant. Such lubricated contact processes are difficult to examine experimentally. Atomistic simulations are an attractive alternative for investigating the fundamentals of such processes. In this work, molecular dynamics simulations were used for studying different elementary processes of lubricated tribological contacts. A simplified, yet realistic simulation setup was developed in this work for that purpose using classical force fields. In particular, the two solid bodies were fully submersed in the fluid lubricant such that the squeeze-out was realistically modeled. The velocity of the relative motion of the two solid bodies was imposed as a boundary condition. Two types of cases were considered in this work: i) a model system based on synthetic model substances, which enables a direct, but generic, investigation of molecular interaction features on the contact process; and ii) real substance systems, where the force fields describe specific real substances. Using the model system i), also the reproducibility of the findings obtained from the computer experiments was critically assessed. In most cases, also the dry reference case was studied. Both mechanical and thermodynamic properties were studied – focusing on the influence of lubrication. The following properties were studied: The contact forces, the coefficient of friction, the dislocation behavior in the solid, the chip formation and the formation of the groove, the squeeze-out behavior of the fluid in the contact zone, the local temperature and the energy balance of the system, the adsorption of fluid particles on the solid surfaces, as well as the formation of a tribofilm. Systematic studies were carried out for elucidating the influence of the wetting behavior, the influence of the molecular architecture of the lubricant, and the influence of the lubrication gap height on the contact process. As expected, the presence of a fluid lubricant reduces the temperature in the vicinity of the contact zone. The presence of the lubricant is, moreover, found to have a significant influence on the friction and on the energy balance of the process. The presence of a lubricant reduces the coefficient of friction compared to a dry case in the starting phase of a contact process, while lubricant molecules remain in the contact zone between the two solid bodies. This is a result of an increased normal and slightly decreased tangential force in the starting phase. When the fluid molecules are squeezed out with ongoing contact time and the contact zone is essentially dry, the coefficient of friction is increased by the presence of a fluid compared to a dry case. This is attributed to an imprinting of individual fluid particles into the solid surface, which is energetically unfavorable. By studying the contact process in a wide range of gap height, the entire range of the Stribeck curve is obtained from the molecular simulations. Thereby, the three main lubrication regimes of the Stribeck curve and their transition regions are covered, namely boundary lubrication (significant elastic and plastic deformation of the substrate), mixed lubrication (adsorbed fluid layers dominate the process), and hydrodynamic lubrication (shear flow is set up between the surface and the asperity). The atomistic effects in the different lubrication regimes are elucidated. Notably, the formation of a tribofilm is observed, in which lubricant molecules are immersed into the metal surface. The formation of a tribofilm is found to have important consequences for the contact process. The work done by the relative motion is found to mainly dissipate and thereby heat up the system. Only a minor part of the work causes plastic deformation. Finally, the assumptions, simplifications, and approximations applied in the simulations are critically discussed, which highlights possible future work.

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“…Asphaltene inhibitors are typically amphiphilic surfactant or dispersant-type molecules. Reported inhibitors include mono-substituted esters of glycerol (Breen, 2001), esters of sorbitan (Spans) (Breen, 2001), alkylamines (Subramanian et al, 2018b), alkylphenols (Chang and Fogler, 1994;Goual et al, 2014;Rogel and León, 2001;Wei et al, 2015), alkylbenzene sulfonates such as dodecylbenzyl sulfonic acid (Benayada and Rahmani, 1999;Chang and Fogler, 1994;Goual and Sedghi, 2015;León et al, 1999;Liu et al, 2015;Wei et al, 2015) and polymeric dispersants such as polyisobutylene succinimides (PIBS) (Breen, 2001;Hashmi et al, 2010;Manek and Sawhney, 1996;Marques et al, 2012;Wang et al, 2017). It has been theorised that resins, which are naturally occurring in crude oil, can stabilise asphaltenes (Acevedo et al, 1995;Kawanaka et al, 1989;Leontaritis and Mansoori, 1987;Pfeiffer and Saal, 1939;Porte et al, 2003;Soorghali et al, 2014), hence chemists may look to utilise these chemistries by finding synthetic analogues or by recycling / reintroducing natural resins (Khvostichenko and Andersen, 2010;Speight, 2004).…”

Section: Introductionmentioning

confidence: 99%

Mechanism of an asphaltene inhibitor in different depositing environments: Influence of colloid stability

Campen

Moorhouse

Wong

2020

Journal of Petroleum Science and Engineering

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Additives are used to reduce unwanted carbonaceous deposits of asphaltenes on surfaces during petroleum production from natural oil and gas reservoirs. The working mechanism of formulated additive packages can be multifaceted. Additives may be effective in the bulk fluid by preventing asphaltenes aggregation, as well as at the surface by preventing asphaltenes adhesion. In this paper, we investigate the numerous different mechanisms by which an asphaltene inhibitor can interfere with the formation of carbonaceous deposits using a combination of techniques including dynamic light scattering to determine particle size distribution, quartz crystal microbalance with dissipation monitoring to examine deposition behaviour and atomic force microscopy to probe deposit morphology. The tested inhibitor prevents deposition of asphaltenes in toluene, where asphaltenes exist as a stable colloidal dispersion of nanoaggregates, by forming barrier-type films that inhibit asphaltenes adhesion and displacing adsorbed thin films of asphaltenes. However, inhibitor performance in heptane-toluene, where asphaltenes are destabilised, depends on the degree of destabilisation. At low heptane volume fraction, inhibitor slows the rate of deposition and deposition rate decreases with increasing inhibitor concentration. However, at high heptane volume fraction, inhibitor can increase the deposition rate, particularly when used in high concentration. At high heptane volume fraction, inhibitor addition alters the morphology of the deposit from that consisting of large flocculent aggregates to that consisting of smaller, submicrometer aggregates. This is consistent with the finding that inhibitor acts as an anti-agglomerant and prevents the formation of large aggregates in the bulk liquid. This paper shows that the impact of inhibitor addition depends on the environmental conditions encountered and the degree of destabilisation of the asphaltenes. Where inhibitor addition alters the nature of depositing species from large flocculent aggregates to smaller submicrometer aggregates, an increase in deposition rate may be observed.

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Interfacial assignment of branched-alkyl benzene sulfonates: A molecular simulation

Abstract: A molecular dynamics study of the breathing and deforming modes of the spherical ionic SDS and nonionic C 12 E 8 micelles

Cited by 17 publications

References 23 publications

Enrichment at vapour–liquid interfaces of mixtures: establishing a link between nanoscopic and macroscopic properties

Enrichment at vapour–liquid interfaces of mixtures: establishing a link between nanoscopic and macroscopic properties

Influence of Lubrication on Tribological Nanoscopic Contact Processes

Mechanism of an asphaltene inhibitor in different depositing environments: Influence of colloid stability

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