Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations

Klein T, Wu W, Rausch MH, Giraudet C, Koller TM, Fröba AP (2018)

Publication Language: English

Publication Status: Published

Publication Type: Journal article, Original article

Publication year: 2018

Journal

Journal of Physical Chemistry B American Chemical Society

Publisher: AMER CHEMICAL SOC

Book Volume: 122

Pages Range: 7122-7133

Journal Issue: 28

DOI: 10.1021/acs.jpcb.8b03568

Abstract

This study contributes to a fundamental understanding of how the liquid structure in a model system consisting of weakly associative n-hexane (n-C6H14) and carbon dioxide (CO2) influences the Fickian diffusion process. For this, the benefits of light scattering experiments and molecular dynamics (MD) simulations at macroscopic thermodynamic equilibrium were combined synergistically. Our reference Fickian diffusivities measured by dynamic light scattering (DLS) revealed an unusual trend with increasing CO2 mole fractions up to about 70 mol %, which agrees with our simulation results. The molecular impacts on the Fickian diffusion were analyzed by MD simulations, where kinetic contributions related to the Maxwell-Stefan (MS) diffusivity and structural contributions quantified by the thermodynamic factor were studied separately. Both the MS diffusivity and the thermodynamic factor indicate the deceleration of Fickian diffusion compared to an ideal mixture behavior. Computed radial distribution functions as well as a significant blue-shift of the CH stretching modes of n-C6H14 identified by Raman spectroscopy show that the slowing down of the diffusion is caused by a structural organization in the binary mixtures over a broad concentration range in the form of self-associated n-C6H14 and CO2 domains. These networks start to form close to the infinite dilution limits and seem to have their largest extent at a solute-solvent transition point at about 70 mol % CO2. The current results not only improve the general understanding of mass diffusion in liquids but also serve to develop sound prediction models for Fick diffusivities.

Authors with CRIS profile

Tobias Klein Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP) Wenchang Wu Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP) Michael Rausch Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP) Cédric Giraudet Erlangen Graduate School in Advanced Optical Technologies (SAOT) Thomas Manfred Koller Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP) Andreas Paul Fröba Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP)

Additional Organisation(s)

Erlangen Graduate School in Advanced Optical Technologies (SAOT)

Related research project(s)

Characterization of molecular diffusion in liquids with dissolved gases April 1, 2016 - June 30, 2019

How to cite

APA:

Klein, T., Wu, W., Rausch, M.H., Giraudet, C., Koller, T.M., & Fröba, A.P. (2018). Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations. Journal of Physical Chemistry B, 122(28), 7122-7133. https://doi.org/10.1021/acs.jpcb.8b03568

MLA:

Klein, Tobias, et al. "Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations." Journal of Physical Chemistry B 122.28 (2018): 7122-7133.

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