Confined thin films of linear and branched alkanes

Dijkstra, Marjolein

doi:10.1063/1.474678

Cited by 82 publications

(64 citation statements)

References 35 publications

(37 reference statements)

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“…The basic CBMC scheme has been extended to branched molecules 50,56,57 and cyclic molecules. [58][59][60][61] The scheme that is discussed here is appropriate for united atom models; for all atom models a slightly different scheme should be used.…”

Section: Configurational-bias Monte Carlomentioning

confidence: 99%

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

2008

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Section: Configurational-bias Monte Carlomentioning

confidence: 99%

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

2008

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“…The following strategies have been used to grow branched molecules. Siepmann et al, 27 and Zhuravlev and Siepmann 73 have used a fixed growth path along the molecule, Cui et al 74 first grow the backbone of a molecule and then insert the side-chains, and Dijkstra 75 grows all groups at a branch simultaneously. The first two approaches implicitly assume that branches connected to the same central atom can be added independently.…”

Section: Appendix B: Details On the Simulation Techniquesmentioning

confidence: 99%

“…The scheme used by Dijkstra 75 in which both atoms are generated simultaneously does not suffer from this problem. In this work we have used a Monte Carlo scheme to generate the trial positions simultaneously.…”

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confidence: 99%

Molecular Simulations of Adsorption Isotherms for Linear and Branched Alkanes and Their Mixtures in Silicalite

1999

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The configurational-bias Monte Carlo (CBMC) technique has been used for computing the adsorption isotherms for linear and branched 2-methylalkanes on silicalite. The carbon numbers of the alkanes ranged from four to nine. For branched alkanes inflection behavior was observed for all carbon numbers studied. The inflection was found to occur at a loading of four molecules per unit cell. Below this loading the branched alkanes are seen to be located predominantly at the intersections of the straight and zigzag channels. To obtain loadings higher than four, the branched alkane must seek residence in the channel interiors which is energetically more demanding and therefore requires disproportionately higher pressures; this leads to the inflection behavior. Linear alkanes with six and more carbon atoms also were found to exhibit inflection behavior. Hexane and heptane show inflection due to commensurate "freezing"; the length of these molecules is commensurate with the length of the zigzag channels. This leads to a higher packing efficiency than for other linear alkanes. Available experimental data from the literature are used to confirm the accuracy of the predictions of the CBMC simulations. Furthermore, the temperature dependency of the isotherms are also properly modeled. For purposes of fitting the isotherms we found that the dual-site Langmuir model provides an excellent description of the simulated isotherms for linear and branched alkanes. In this model we distinguish between two sites with differing ease of adsorption: site A, representing the intersections between the straight and zigzag channels, and site B, representing the channel interiors. CBMC simulations of isotherms of 50-50 binary mixtures of C 5 , C 6 , and C 7 hydrocarbon isomers show some remarkable and hitherto unreported features. The loading of the branched isomer in all three binary mixtures reaches a maximum when the total mixture loading corresponds to four molecules per unit cell. Higher loadings are obtained by "squeezing out" of the branched alkane from the silicalite and replacing these with the linear alkane. This "squeezing out" effect is found to be entropic in nature; the linear alkanes have a higher packing efficiency and higher loadings are more easily achieved by replacing the branched alkanes with the linear alkanes. The mixture isotherms can be predicted quite accurately by applying the appropriate mixture rules to the dual-site Langmuir model. This model allows the mixture isotherm to be predicted purely on the basis of the parameters describing the isotherms of the pure components. The sorption selectivity exhibited by silicalite for the linear alkane in preference to the branched alkane in mixtures of C 5 , C 6 , and C 7 hydrocarbon isomers, provides a potential for the development of a novel separation technique based on entropy-driven sorption selectivity.

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“…However, in our calculations we ignore the corrugation of the surfaces and we used the smooth potential. For more detail on the precise values of the potential parameters, we refer the reader to [33].…”

Section: Simulationsmentioning

confidence: 99%

Structure and solvation forces in confined films of alkanes

Dijkstra¹

1998

Thin Solid Films

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We compute by computer simulations the solvation force of a system of linear and branched alkanes confined in a slab geometry. The solvation force for linear decane oscillates with distance with a periodicity close to the width of the molecules. The branched alkanes, 2-methylundecane and 2-methylheptane, show a similar oscillatory behaviour, however the oscillations are decreased with a factor of about three and show a long-range attractive force. In addition, we show that the critical temperature of the liquid-vapour coexistence of npentane shifts to lower temperatures upon confining.

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Confined thin films of linear and branched alkanes

Cited by 82 publications

References 35 publications

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

Molecular Simulations of Adsorption Isotherms for Linear and Branched Alkanes and Their Mixtures in Silicalite

Structure and solvation forces in confined films of alkanes

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