Controlled shrinkage and re-expansion of a single aqueous droplet inside an optical vortex trap
Controlled shrinkage and re-expansion of a single aqueous droplet inside an optical vortex trap
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DOI：
10.1021/jp068902v
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发表时间：
2007-03-22
影响因子：
3.3
通讯作者：
Chiu, Daniel T.
中科院分区：
文献类型：
--
作者：
Jeffries, Gavin D. M.;Kuo, Jason S.;Chiu, Daniel T.
本文描述了悬浮在有机介质中并保持在光学涡旋阱中的单个飞升体积的水液滴的收缩和再膨胀。为了阐明这一现象背后的机制，我们构建了一个传热传质模型，并进行了实验验证我们的模型。从这些研究中，我们得出结论，蒸发机制充分描述了在涡流阱中保持的含水液滴的收缩，而基于由围绕液滴的水引起的有机相的过饱和的机制充分解释了收缩液滴的再膨胀。所提出的机制与使用不同的有机介质的实验观察，当H2O被替换为D2 O，当使用光镊诱导液滴收缩，而不是一个光学涡旋陷阱。对于H2O液滴，在收缩过程中液滴内的温度上升是在1 K或更低的数量级，由于热量的快速热传导远离液滴在微尺度和急剧增加的溶解度的水的有机相的温度略有升高。由于限制在液滴中的大多数化学物质可以被制成对水/有机界面不可渗透，因此水性液滴体积的变化转化为液滴内溶解物质浓度的变化。因此，这种现象应该在对浓度敏感的基本化学过程的研究中找到用途，例如大分子拥挤和蛋白质成核和结晶。
This paper describes the shrinkage and re-expansion of individual femtoliter-volume aqueous droplets that were suspended in an organic medium and held in an optical vortex trap. To elucidate the mechanism behind this phenomenon, we constructed a heat- and mass-transfer model and carried out experimental verifications of our model. From these studies, we conclude that an evaporation mechanism sufficiently describes the shrinkage of aqueous droplets held in a vortex trap, whereas a mechanism based on the supersaturation of the organic phase by water that surrounds the droplet adequately explains the re-expansion of the shrunk droplet. The proposed mechanisms correlated well with experimental observations using different organic media, when H2O was replaced with D2O and when an optical tweezer was used to induce droplet shrinkage rather than an optical vortex trap. For H2O droplets, the temperature rise within the droplet during shrinkage was on the order of 1 K or less, owing to the rapid thermal conduction of heat away from the droplet at the microscale and the sharp increase in solubility for water by the organic phase with slight elevations in temperature. Because most chemical species confined to droplets can be made impenetrable to the aqueous/organic interface, a change in the volume of aqueous droplets translates into a change in concentration of the dissolved species within the droplets. Therefore, this phenomenon should find use in the study of fundamental chemical processes that are sensitive to concentration, such as macromolecular crowding and protein nucleation and crystallization.