Existence of micrometer-scale water droplets at solvent/air interfaces.
Existence of micrometer-scale water droplets at solvent/air interfaces.
复制标题
溶剂/空气界面处存在微米级水滴。
DOI：
10.1021/la302420s
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
J. Boland
中科院分区：
文献类型：
--
作者：
Rónán Daly;J. Sader;J. Boland
使用纯液体的文献值的标准表面能平衡预测水滴在许多常见有机溶剂的液体/空气界面处是不稳定的。虽然已经研究了溶剂存在下宏观液滴的行为，但对微米尺寸范围内的液滴以及线张力可能的作用的研究却明显缺乏。在这篇文章中，我们实验研究的存在和稳定性，这种微米级的液滴形成在空气/溶剂界面和可能的作用所发挥的部分溶解度的有机液体在水中和溶剂的迁移，在降低的关键空气/水的表面张力。研究了三种溶剂：甲苯、乙酸丁酯和氯仿，使用光学监测水微滴在空气/溶剂表面上的冷凝和手动沉积的技术。这证明了稳定水滴的存在，并允许测量溶剂/水/空气界面处的接触角。接触角与液滴尺寸（直径：2-30 μm）无关，排除了半径大于1 μm的液滴的线张力稳定机制。沉积的水滴的界面张力独立地测量使用等效的宏观实验，其产生与甲苯和乙酸丁酯在水中的部分溶解性一致的结果。氯仿，可能的机制进行了讨论，观察到的差异。
Standard surface energy balances using literature values for pure liquids predict that water droplets are unstable at the liquid/air interfaces of many common organic solvents. While the behavior of macroscopic drops in the presence of solvents has been studied, the study of droplets in the micrometer size regime and the possible role of line tension are notably absent. In this article, we experimentally investigate the existence and stability of such micrometer-scale droplets formed at air/solvent interfaces and the possible roles played by partial solubility of organic liquids in water and solvent migration in the lowering of the key air/water surface tension. Three solvents are studied: toluene, butyl acetate, and chloroform, using a technique to optically monitor both condensation and manual deposition of water microdroplets onto air/solvent surfaces. This demonstrates both the existence of stable water droplets and allows measurement of the contact angles at the solvent/water/air interface. Contact angles are shown to be independent of droplet size (diameters: 2-30 μm), ruling out a line tension stabilization mechanism for droplets of radii greater than 1 μm. The interfacial tensions of the deposited water droplets are independently measured using an equivalent macroscopic experiment, which yield results consistent with the partial miscibility of toluene and butyl acetate in water. A discrepancy is observed for chloroform, for which possible mechanisms are discussed.