Université de Reims Champagne-Ardenne, CNRS, GSMA UMR 7331, 51097 Reims, France.
Molecules. 2021 Mar 19;26(6):1711. doi: 10.3390/molecules26061711.
The diffusion of carbon dioxide (CO2) and ethanol (EtOH) is a fundamental transport process behind the formation and growth of CO2 bubbles in sparkling beverages and the release of organoleptic compounds at the liquid free surface. In the present study, CO2 and EtOH diffusion coefficients are computed from molecular dynamics (MD) simulations and compared with experimental values derived from the Stokes-Einstein (SE) relation on the basis of viscometry experiments and hydrodynamic radii deduced from former nuclear magnetic resonance (NMR) measurements. These diffusion coefficients steadily increase with temperature and decrease as the concentration of ethanol rises. The agreement between theory and experiment is suitable for CO2. Theoretical EtOH diffusion coefficients tend to overestimate slightly experimental values, although the agreement can be improved by changing the hydrodynamic radius used to evaluate experimental diffusion coefficients. This apparent disagreement should not rely on limitations of the MD simulations nor on the approximations made to evaluate theoretical diffusion coefficients. Improvement of the molecular models, as well as additional NMR measurements on sparkling beverages at several temperatures and ethanol concentrations, would help solve this issue.
二氧化碳（CO2）和乙醇（EtOH）的扩散是起泡饮料中 CO2 气泡形成和生长以及液体自由表面释放感官化合物的基本传输过程。在本研究中，从分子动力学（MD）模拟中计算 CO2 和 EtOH 的扩散系数，并基于粘度实验和从前核磁共振（NMR）测量推导出的流体力学半径，根据 Stokes-Einstein（SE）关系将其与实验值进行比较。这些扩散系数随温度升高而稳定增加，随乙醇浓度升高而降低。理论与实验之间的一致性适用于 CO2。理论 EtOH 扩散系数略倾向于高估实验值，尽管通过改变用于评估实验扩散系数的流体力学半径可以改善这种一致性。这种明显的不一致不应依赖于 MD 模拟的限制，也不应依赖于评估理论扩散系数所做的近似。改进分子模型，以及在几个温度和乙醇浓度下对 sparkling beverages 进行更多的 NMR 测量，将有助于解决这个问题。
