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,The Journal of Physical Chemistry B

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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
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2018-07-03 , DOI: 10.1021/acs.jpcb.8b03568
Tobias Klein ₁ , Wenchang Wu ₁ , Michael H. Rausch ₁ , Cédric Giraudet ₁ , Thomas M. Koller ₁ , Andreas P. Fröba ₁

Affiliation

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.

中文翻译：

在菲克扩散液结构中的二元混合物的影响ñ正己烷和二氧化碳的探索Sun Yatsen动态光散射，拉曼光谱和分子动力学模拟

此研究有助于在一个模型系统中的液体结构，其中包括弱缔合的如何的基本理解Ñ己烷（Ñ -C ₆ ħ ₁₄）和二氧化碳（CO ₂）影响菲克扩散过程。为此，将宏观热力学平衡条件下的光散射实验和分子动力学（MD）模拟的好处进行了协同组合。我们通过动态光散射（DLS）测量的参考菲克扩散率显示出CO ₂升高的异常趋势摩尔分数高达约70 mol％，这与我们的模拟结果相符。通过MD模拟分析了分子对Fickian扩散的影响，其中分别研究了与Maxwell–Stefan（MS）扩散率有关的动力学贡献和由热力学因子量化的结构贡献。与理想的混合行为相比，MS扩散率和热力学因子都表明菲克扩散的减速度。计算的径向分布函数以及n -C ₆ H ₁₄的CH拉伸模式的显着蓝移通过拉曼光谱法鉴定的结果表明，扩散的减慢是由二元混合物中自相关n -C ₆ H ₁₄和CO ₂结构域形式的二元混合物中的结构组织引起的。这些网络开始形成接近无限稀释极限，并且似乎在溶质-溶剂转变点（约70 mol％CO _2）具有最大程度的扩散。目前的结果不仅增进了人们对液体中质量扩散的一般理解，而且还有助于建立针对Fick扩散率的声音预测模型。

更新日期：2018-07-04

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