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Journal of Chemical Physics / Volume 131 / Issue 16 / COMMUNICATIONS
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J. Chem. Phys. 131, 161101 (2009); http://dx.doi.org/10.1063/1.3256235 (4 pages)

Composition and concentration anomalies for structure and dynamics of Gaussian-core mixtures

Mark J. Pond1, William P. Krekelberg1, Vincent K. Shen2, Jeffrey R. Errington3, and Thomas M. Truskett1,4

1Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
2Chemical and Biochemical Reference Data Division, National Institute of Standards and Technology, Gaithersburg, Maryland 02899-8320, USA
3Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200, USA
4Institute for Theoretical Chemistry, University of Texas at Austin, Austin, Texas 78712, USA

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(Received 3 September 2009; accepted 7 October 2009; published online 22 October 2009)

We report molecular dynamics simulation results for two-component fluid mixtures of Gaussian-core particles, focusing on how tracer diffusivities and static pair correlations depend on temperature, particle concentration, and composition. At low particle concentrations, these systems behave like simple atomic mixtures. However, for intermediate concentrations, the single-particle dynamics of the two species largely decouple, giving rise to the following anomalous trends. Increasing either the concentration of the fluid (at fixed composition) or the mole fraction of the larger particles (at fixed particle concentration) enhances the tracer diffusivity of the larger particles but decreases that of the smaller particles. In fact, at sufficiently high particle concentrations, the larger particles exhibit higher mobility than the smaller particles. Each of these dynamic behaviors is accompanied by a corresponding structural trend that characterizes how either concentration or composition affects the strength of the static pair correlations. Specifically, the dynamic trends observed here are consistent with a single empirical scaling law that relates an appropriately normalized tracer diffusivity to its pair-correlation contribution to the excess entropy.

© 2009 American Institute of Physics

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KEYWORDS and PACS

Keywords

diffusion, entropy, liquid structure, molecular dynamics method

PACS

  • 61.20.Ja

    Computer simulation of liquid structure

  • 65.20.-w

    Thermal properties of liquids

  • 61.25.-f

    Studies of specific liquid structures

  • 66.10.C-

    Diffusion and thermal diffusion

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3256235

PUBLICATION DATA

ISSN

0021-9606 (print)  
1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

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  36. See EPAPS supplementary material at http://www.aip.org/pubservs/epaps.html http://dx.doi.org/10.1063/1.3256235 for tracer diffusivity and structural order metric date versus concentration for the binary Gaussian-core fluid mixture discussed in the text at different mole fractions and temperatures. [EPAPS]

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Figures (click on thumbnails to view enlargements)

FIG.1
(a) Tracer diffusivity Di and (b) structural order metric −si(2), with i ∊ {A,B}, vs concentration ρσAA3 for the binary GC fluid mixture discussed in the text. The collective structural order metric −s(2) is also included in (b). The temperature is kBT/ϵAA = 0.1 and the mole fraction is xA = 0.5.

FIG.1 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.2
Rosenfeld scaled tracer diffusivity DiR = Diρ1/3(kBT/mi)−1/2 vs (a) two-body excess entropy −s(2) and (b) its contribution from structuring around type i particles −si(2), with i ∊ {A,B}, for the binary GC fluid mixture discussed in the text. Shown are mole fractions xA = 0.1 (black), 0.3 (red), 0.5 (orange), 0.7 (blue), and 0.9 (green) and temperatures kBT/ϵAA = 0.05 (○), 0.1 (◻), 0.2 (◇), and 0.4 (▽). Filled and open shapes represent A and B particles, respectively. The dashed line indicates a least-square fit to a power law relationship for the single-component GC fluid (Ref. 9), DR = 0.208s(2)−0.972.

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FIG.3
Tracer diffusivity Di for (a) A particles and (b) B particles and structural order metric −si(2) for (c) A particles and (d) B particles for the binary GC mixture discussed in the text. All are plotted versus density ρσAA3. Data shown are for temperature kBT/ϵAA = 0.2 and mole fractions xA = 0.1, 0.3, 0.5, 0.7, and 0.9. Arrows indicate increasing xA. The dashed lines separate the approximate low, intermediate, and high density ranges described in the text.

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

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