Yu Xiaoqing, Seki Takakazu, Yu Chun-Chieh, Zhong Kai, Sun Shumei, Okuno Masanari, Backus Ellen H G, Hunger Johannes, Bonn Mischa, Nagata Yuki
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
University of Groningen, Zernike Institute for Advanced Materials, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
J Phys Chem B. 2021 Sep 23;125(37):10639-10646. doi: 10.1021/acs.jpcb.1c06001. Epub 2021 Sep 10.
The evaporation of molecules from water-organic solute binary mixtures is key for both atmospheric and industrial processes such as aerosol formation and distillation. Deviations from ideal evaporation energetics can be assigned to intermolecular interactions in solution, yet evaporation occurs from the interface, and the poorly understood interfacial, rather than the bulk, structure of binary mixtures affects evaporation kinetics. Here we determine the interfacial structure of nonideal binary mixtures of water with methanol, ethanol, and formic acid, by combining surface-specific vibrational spectroscopy with molecular dynamics simulations. We find that the free, dangling OH groups at the interfaces of these differently behaving nonideal mixtures are essentially indistinguishable. In contrast, the ordering of hydrogen-bonded interfacial water molecules differs substantially at these three interfaces. Specifically, the interfacial water molecules become more disordered (ordered) in mixtures with methanol and ethanol (formic acid), showing higher (lower) vapor pressure than that predicted by Raoult's law.
水 - 有机溶质二元混合物中分子的蒸发对于大气和工业过程（如气溶胶形成和蒸馏）都至关重要。与理想蒸发能量学的偏差可归因于溶液中的分子间相互作用，然而蒸发是从界面发生的，二元混合物中 poorly understood（此处可能有误，推测为“理解不足的”）界面结构而非本体结构影响蒸发动力学。在这里，我们通过将表面特异性振动光谱与分子动力学模拟相结合，确定了水与甲醇、乙醇和甲酸的非理想二元混合物的界面结构。我们发现，在这些表现不同的非理想混合物界面处的游离、悬空的OH基团基本上无法区分。相比之下，在这三个界面处，氢键连接的界面水分子的排列有很大差异。具体而言，与甲醇和乙醇（甲酸）混合时，界面水分子变得更加无序（有序），其蒸气压高于（低于）拉乌尔定律预测的值。
