Comparison of United-Atom Potentials for the Simulation of Vapor鈥揕iquid Equilibria and Interfacial Properties of Long-Chain n-Alkanes up to n-C100

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• 作者：Erich A. M眉ller ; Andr茅s Mej铆a
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：November 10, 2011
• 年：2011
• 卷：115
• 期：44
• 页码：12822-12834
• 全文大小：1080K
• 年卷期：v.115,no.44(November 10, 2011)
• ISSN：1520-5207

文摘

Canonical ensemble molecular dynamics (MD) simulations are reported which compute both the vapor鈥搇iquid equilibrium properties (vapor pressure and liquid and vapor densities) and the interfacial properties (density profiles, interfacial tensions, entropy and enthalpy of surface formation) of four long-chained n-alkanes: n-decane (n-C₁₀), n-eicosane (n-C₂₀), n-hexacontane (n-C₆₀), and n-decacontane (n-C₁₀₀). Three of the most commonly employed united-atom (UA) force fields for alkanes (SKS: Smit, B.; Karaborni, S.; Siepmann, J. I. J. Chem. Phys. 1995,102, 2126鈥?140; J. Chem. Phys. 1998,109, 352; NERD: Nath, S. K.; Escobedo, F. A.; de Pablo, J. J. J. Chem. Phys. 1998, 108, 9905鈥?911; and TraPPE: Martin M. G.; Siepmann, J. I. J. Phys. Chem. B1998, 102, 2569鈥?577.) are critically appraised. The computed results have been compared to the available experimental data and those fitted using the square gradient theory (SGT). In the latter approach, the Lennard鈥揓ones chain equation of state (EoS), appropriately parametrized for long hydrocarbons, is used to model the homogeneous bulk phase Helmholtz energy. The MD results for phase equilibria of n-decane and n-eicosane exhibit sensible agreement both to the experimental data and EoS correlation for all potentials tested, with the TraPPE potential showing the lowest deviations. However, as the molecular chain increases to n-hexacontane and n-decacontane, the reliability of the UA potentials decreases, showing notorious subpredictions of both saturated liquid density and vapor pressure. Based on the recommended data and EoS results for the heaviest hydrocarbons, it is possible to attest, that in this extreme, the TraPPE potential shows the lowest liquid density deviations. The low absolute values of the vapor pressure preclude the discrimination among the three UA potentials studied. On the other hand, interfacial properties are very sensitive to the type of UA potential thus allowing a differentiation of the potentials. Comparing the interfacial tension MD results to the available experimental data and SGT results, the TraPPE model exhibits the lowest deviations for all hydrocarbons.