A molecular dynamics study on transport properties and structure at the liquid–vapor interfaces of alkanes

Chilukoti, Hari Krishna; Kikugawa, Gota; Ohara, Taku

doi:10.1016/j.ijheatmasstransfer.2012.12.015

Cited by 32 publications

(21 citation statements)

References 34 publications

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“…This deficiency in FFs in such a situation is related to the fact that the internal rotations or torsions of long chain molecules are parameterized using FFs based on a single conformer, while characterizations of these sorts of internal molecular dynamics in the hydrocarbon molecules, the main components of fuel droplets, with multi-structural effects change from one another 10 . This is supported by the results obtained for orientation of n -alkanes at the centre of interfacial layer using non-reactive MD simulations and experimental results 11 12 13 . Using the vibrational sum frequency spectroscopy (VSFS), which is widely applied to determine molecular orientations at the interfaces, it can be shown that the chain of n -alkane molecules from n -nonane (C 9 H 20 ) to n -hexadecane (C 16 H 34 ) are perpendicular to the surface 13 at the temperatures well above the melting points.…”

supporting

confidence: 73%

Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

Nasiri

2016

Sci Rep

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The role of boundary conditions at the interface for both Boltzmann equation and the set of Navier-Stokes equations have been suggested to be important for studying of multiphase flows such as evaporation/condensation process which doesn’t always obey the equilibrium conditions. Here we present aspects of transition-state theory (TST) alongside with kinetic gas theory (KGT) relevant to the study of quasi-equilibrium interfacial phenomena and the equilibrium gas phase processes, respectively. A two-state mathematical model for long-chain hydrocarbons which have multi-structural specifications is introduced to clarify how kinetics and thermodynamics affect evaporation/condensation process at the surface of fuel droplet, liquid and gas phases and then show how experimental observations for a number of n-alkane may be reproduced using a hybrid framework TST and KGT with physically reasonable parameters controlling the interface, gas and liquid phases. The importance of internal activation dynamics at the surface of n-alkane droplets is established during the evaporation/condensation process.

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supporting

confidence: 73%

Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

Nasiri

2016

Sci Rep

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“…MD simulations allow the study of systems under phase equilibrium and specifically can be applied to examine the contributions due to intramolecular and intermolecular interactions to the thermophysical properties directly at the equilibrium interface and also at their corresponding bulk phases [10][11][12][13][14]. The simulation of the coexisting VLE uses pair-effective intermolecular potentials that are capable of reproducing their thermophysical properties [7,15,16] and transport properties for simple fluids [17][18][19]. The VLE of ethane was simulated using the MD methodology (in-house code) in the range of 100-260 K. The simulations were carried out using the Verlet algorithm with a Nose thermostat [20] and a time step of 1 fs.…”

Section: Methodsmentioning

confidence: 99%

The Intramolecular Pressure and the Extension of the Critical Point’s Influence Zone on the Order Parameter

Rivera

Nicanor-Guzman

Guerra-González

2015

Advances in Condensed Matter Physics

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The critical point affects the coexistence behavior of the vapor-liquid equilibrium densities. The length of the critical influence zone is under debate because for some properties, like shear viscosity, the extension is only a few degrees, while for others, such as the density order parameter, the critical influence zone covers up to hundreds of degrees below the critical temperature. Here we show that, for ethane, the experimental critical influence zone covers a wide zone of tens of degrees (below the critical temperature) down to a transition temperature, at which the apparent critical influence zone vanishes, and the transition temperature can be predicted through a pressure analysis of the coexisting bulk liquid phase, using a simple molecular potential. The liquid phases within the apparent critical influence zone show low densities, making them behave internally like their corresponding vapor phases. Therefore, Molecular Dynamics simulations reveal that the experimentally observed wide extension of the critical influence zone is the result of a vapor-like effect due to low bulk liquid phase densities.

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“…Additionally, the surface ordering decreases with increasing temperature, and the orientation behavior at the interface for all examined molecules is similar to that reported for chain molecules, such as perfluorinated alkanes, fluorocarbons, semifluorinated alkanes, and hydrocarbon n-alkanes. [38][39][40][41] The observation that the condensation/evaporation coefficient is close to unity at low temperatures and decreases with increasing temperature implies that the effect of surface ordering on the condensation/evaporation coefficient is insignificant.…”

Section: Molecular Orientationmentioning

confidence: 99%

Molecular dynamics study on condensation/evaporation coefficients of chain molecules at liquid–vapor interface

Nagayama

Takematsu

Mizuguchi

et al. 2015

The Journal of Chemical Physics

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The structure and thermodynamic properties of the liquid-vapor interface are of fundamental interest for numerous technological implications. For simple molecules, e.g., argon and water, the molecular condensation/evaporation behavior depends strongly on their translational motion and the system temperature. Existing molecular dynamics (MD) results are consistent with the theoretical predictions based on the assumption that the liquid and vapor states in the vicinity of the liquid-vapor interface are isotropic. Additionally, similar molecular condensation/evaporation characteristics have been found for long-chain molecules, e.g., dodecane. It is unclear, however, whether the isotropic assumption is valid and whether the molecular orientation or the chain length of the molecules affects the condensation/evaporation behavior at the liquid-vapor interface. In this study, MD simulations were performed to study the molecular condensation/evaporation behavior of the straight-chain alkanes, i.e., butane, octane, and dodecane, at the liquid-vapor interface, and the effects of the molecular orientation and chain length were investigated in equilibrium systems. The results showed that the condensation/evaporation behavior of chain molecules primarily depends on the molecular translational energy and the surface temperature and is independent of the molecular chain length. Furthermore, the orientation at the liquid-vapor interface was disordered when the surface temperature was sufficiently higher than the triple point and had no significant effect on the molecular condensation/evaporation behavior. The validity of the isotropic assumption was confirmed, and we conclude that the condensation/evaporation coefficients can be predicted by the liquid-to-vapor translational length ratio, even for chain molecules.

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A molecular dynamics study on transport properties and structure at the liquid–vapor interfaces of alkanes

Cited by 32 publications

References 34 publications

Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

The Intramolecular Pressure and the Extension of the Critical Point’s Influence Zone on the Order Parameter

Molecular dynamics study on condensation/evaporation coefficients of chain molecules at liquid–vapor interface

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