Molecular Simulation of Concurrent Gas−Liquid Interfacial Adsorption and Partitioning in Gas−Liquid Chromatography

Wick, Collin D.; Siepmann, J. Ilja; Schure, Mark R.

doi:10.1021/ac0200116

Cited by 35 publications

(37 citation statements)

References 59 publications

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“…[25][26][27][28] As expected, they found that the squalanevapor interface does not appear to be molecularly sharp. Squalane molecules protrude through the interface, and the density profile declines to the vacuum value over a significant distance.…”

Section: Introductionsupporting

confidence: 64%

“…Simulations were performed using the TraPPE (transferable potential for phase equilibria) force field developed by Siepmann and coworkers. [25][26][27][28] A united atom model was used to describe all the CH 3 , CH 2 , and CH units. All simulations were performed in the NVT ensemble using the program DL_POLY2 on an Intel Xeon 3.0 GHz dual processor workstation.…”

Section: Experimental Technique and Simulation Methodsmentioning

confidence: 99%

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Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(³P)(g) with Liquid Squalane

et al. 2007

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The relative reactivity of the liquid surface of a long-chain, partially branched hydrocarbon (squalane, C 30 H 62 ) with gas-phase O( 3 P) atoms has been measured as a function of liquid temperature. The O( 3 P) atoms were generated with a superthermal velocity distribution by 355 nm photolysis of NO 2 . Laser-induced fluorescence was used to detect the relative branching into specific OH product vibrational states. The yield of OH(V′)0) proves significantly less dependent on liquid surface temperature than the yield of OH(V′)1). Time-of-flight measurements of the escaping OH provide partially resolved product translational energy distributions. These profiles also differ between OH vibrational states. OH(V′)1) shows overall longer arrival times, but with a clear trend toward earlier times as the surface temperature is increased. OH(V′)0) shows little detectable variation of the distribution of arrival times over the range of temperatures investigated (263-333 K). We discuss the interpretation of these findings, taking account of earlier experimental work, which has indicated significant contributions from distinct "direct" and "trapping-desorption" reaction mechanisms, and new molecular dynamics simulations of the surface structure. There are a number of factors that may contribute, including both energetic and structural effects. It is not possible on the basis of the current evidence to discriminate conclusively between them. Nevertheless, we conclude, on balance, that structural effects may well be the more important. In particular, higher temperatures are predicted to promote more open structures. We speculate that this may enable more OH(V′)1) to escape before it is either vibrationally relaxed or, less probably, undergoes vibrationally enhanced reaction to produce H 2 O.

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Section: Introductionsupporting

confidence: 64%

Section: Experimental Technique and Simulation Methodsmentioning

confidence: 99%

Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(³P)(g) with Liquid Squalane

et al. 2007

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“…Figure 1 shows that the density of liquid alkane peaks at about 0.5 nm from that interface. The existence of interfacial density peaks has been previously reported for other alkanes [101,102]. The density peaks are sharper at the nonane-water interface than at the nonane-vacuum interface.…”

Section: Interfacial Orientation Of Liquid Alkanes Is Controlled By Tsupporting

confidence: 64%

Strength of Alkane–Fluid Attraction Determines the Interfacial Orientation of Liquid Alkanes and Their Crystallization through Heterogeneous or Homogeneous Mechanisms

Qiu

Molinero

2017

Crystals

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Abstract:Alkanes are important building blocks of organics, polymers and biomolecules. The conditions that lead to ordering of alkanes at interfaces, and whether interfacial ordering of the molecules leads to heterogeneous crystal nucleation of alkanes or surface freezing, have not yet been elucidated. Here we use molecular simulations with the united-atom OPLS and PYS alkane models and the mW water model to determine what properties of the surface control the interfacial orientation of alkane molecules, and under which conditions interfacial ordering results in homogeneous or heterogeneous nucleation of alkane crystals, or surface freezing above the melting point. We find that liquid alkanes present a preference towards being perpendicular to the alkane-vapor interface and more parallel to the alkane-water interface. The orientational order in the liquid is short-ranged, decaying over~1 nm of the surface, and can be reversed by tuning the strength of the attractions between alkane and the molecules in the other fluid. We show that the strength of the alkane-fluid interaction also controls the mechanism of crystallization and the face of the alkane crystal exposed to the fluid: fluids that interact weakly with alkanes promote heterogeneous crystallization and result in crystals in which the alkane molecules orient perpendicular to the interface, while crystallization of alkanes in the presence of fluids, such as water, that interact more strongly with alkanes is homogeneous and results in crystals with the molecules oriented parallel to the interface. We conclude that the orientation of the alkanes at the crystal interfaces mirrors that in the liquid, albeit more pronounced and long-ranged. We show that the sign of the binding free energy of the alkane crystal to the surface, ∆G bind , determines whether the crystal nucleation is homogeneous (∆G bind ≥ 0) or heterogeneous (∆G bind < 0). Our analysis indicates that water does not promote heterogeneous crystallization of the alkanes because water stabilizes more the liquid than the crystal phase of the alkane, resulting in ∆G bind > 0. While ∆G bind < 0 suffices to produce heterogeneous nucleation, the condition for surface freezing is more stringent, ∆G bind < −2 γ xl , where γ xl is the surface tension of the liquid-crystal interface of alkanes. Surface freezing of alkanes is favored by their small value of γ xl . Our findings are of relevance to understanding surface freezing in alkanes and to develop strategies for controlling the assembly of chain-like molecules at fluid interfaces.

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“…This method can also be modified in order to study the liquid-liquid equilibria between two immiscible liquids [19,20]. The use of boxes with interface in the Gibbs Ensemble Monte Carlo also represents a powerful technique which enables us to study the properties of interfaces between vapor and saturated solution of two immiscible liquids [21][22][23]. Molecular Dynamics (MD) simulations in such boxes were also used in studying the free surface of alkane oligomers [24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Inhomogeneous Monte Carlo simulation of the vapor-liquid equilibrium of benzene between 300 K and 530 K

Janeček¹,

Krienke²,

Schmeer³

2007

Condens. Matter Phys.

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The inhomogeneous Monte Carlo technique is used in studying the vapor-liquid interface of benzene in a broad range of temperatures using the TraPPE potential field. The obtained values of the VLE parameters are in good agreement with the experimental values as well as with the results from GEMC simulations. In contrast to the GEMC, within one simulation box the inhomogeneous MC technique also yields information on the structural properties of the interphase between the two phases. The values of the vaporization enthalpy and the vapor pressure very well satisfy the Clausius-Clapeyron equation.

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Molecular Simulation of Concurrent Gas−Liquid Interfacial Adsorption and Partitioning in Gas−Liquid Chromatography

Cited by 35 publications

References 59 publications

Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(³P)(g) with Liquid Squalane

Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(³P)(g) with Liquid Squalane

Strength of Alkane–Fluid Attraction Determines the Interfacial Orientation of Liquid Alkanes and Their Crystallization through Heterogeneous or Homogeneous Mechanisms

Inhomogeneous Monte Carlo simulation of the vapor-liquid equilibrium of benzene between 300 K and 530 K

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Molecular Simulation of Concurrent Gas−Liquid Interfacial Adsorption and Partitioning in Gas−Liquid Chromatography

Cited by 35 publications

References 59 publications

Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(3P)(g) with Liquid Squalane

Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(3P)(g) with Liquid Squalane

Strength of Alkane–Fluid Attraction Determines the Interfacial Orientation of Liquid Alkanes and Their Crystallization through Heterogeneous or Homogeneous Mechanisms

Inhomogeneous Monte Carlo simulation of the vapor-liquid equilibrium of benzene between 300 K and 530 K

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Product

Resources

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Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(³P)(g) with Liquid Squalane

Temperature Dependence of OH Yield, Translational Energy, and Vibrational Branching in the Reaction of O(³P)(g) with Liquid Squalane