Characterization of molecular diffusion in liquids with dissolved gases

拟议的研究项目应有助于从根本上理解由液体和溶解气体组成的二元系统中的分子扩散。为了表征分子扩散，动态光散射（DLS）实验和分子动力学（MD）模拟都应该与系统选择的气液体系相结合。在宏观热力学平衡下研究这类流体时，两种方法都利用了微观波动。这些波动的时间行为由输运系数自扩散率、麦克斯韦-斯蒂芬扩散率和互扩散率决定。DLS从大量流体中确定的相互扩散系数用于验证MD模拟的结果，而MD模拟通过提供对分子流体结构的深入了解来支持DLS数据的解释。为了获得气体在液体中的分子扩散的全面信息，应该在广泛的温度和组成范围内研究具有不同分子大小和相互作用并覆盖广泛混合物粘度的液体和气体的吉祥组合。DLS实验和MD模拟不仅应该为这类系统提供可靠的扩散系数数据库。最重要的是，这些结果应该用于分析混合组分的物理特性对分子扩散的影响。相互扩散率预测的MD模拟性能需要通过与实验结果的比较来检验。为此，必须分别计算麦克斯韦-斯蒂芬扩散系数和热力学因子。MD仿真结果也证明了所研究系统的不同扩散系数是如何相互关联的。此外，从提出的DLS实验和MD模拟中获得的知识应该有助于开发一个简单的预测工程模型，用于液体与溶解气体的二元混合物的相互扩散率。

The proposed research project should contribute to a fundamental understanding of molecular diffusion in binary systems consisting of liquids and dissolved gases. For the characterization of molecular diffusion, both dynamic light scattering (DLS) experiments and Molecular Dynamics (MD) simulations should be used in connection with systematically selected gas-liquid systems. Investigating such fluids at macroscopic thermodynamic equilibrium, both methods make use of microscopic fluctuations. The temporal behavior of these fluctuations is governed by the transport coefficients self-diffusivity, Maxwell-Stefan diffusivity, and mutual diffusivity. The mutual diffusivities determined by DLS from the bulk of fluids serve to verify the results from MD simulations while the latter support the interpretation of the DLS data by providing close insight into the molecular fluid structures. To get comprehensive information on the molecular diffusion of gases in liquids, auspicious combinations of liquids and gases with varying molecular sizes and interactions and covering a wide range of mixture viscosities should be studied over broad ranges of temperature and composition. The DLS experiments and MD simulations should not only provide a reliable database of diffusivities for such systems. Above all, the results should be used for analyzing how molecular diffusion is influenced by the physical characteristics of the mixture components. The performance of MD simulations regarding the prediction of mutual diffusivities should be tested by comparison with the experimental results. For this, the Maxwell-Stefan diffusivity and the thermodynamic factor have to be calculated independently. With the MD simulation results, it can also be proven how the different diffusivities are related to each other for the studied systems. Furthermore, the knowledge obtained from the proposed DLS experiments and MD simulations should contribute to the development of a simple predictive engineering model for the mutual diffusivity of binary mixtures of liquids with dissolved gases.