Does the emulsification procedure influence freezing and thawing of aqueous droplets?
Does the emulsification procedure influence freezing and thawing of aqueous droplets?
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DOI：
10.1063/1.4965434
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发表时间：
2016-12-21
影响因子：
4.4
通讯作者：
Loerting, Thomas
中科院分区：
文献类型：
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作者：
Hauptmann, Astrid;Handle, Karl F.;Loerting, Thomas
在这里，我们研究了水溶液在油乳剂中的冻结和融化特性，特别是考察了油和表面活性剂以及乳状液的搅拌时间的影响。具体地说，我们用光学冷冻显微镜结合差示扫描量热仪研究了乳化的25wt.%硫酸铵液滴在93K温度范围内的相行为，得出了成核温度不随油-表面活性剂组合而变化的结论，即探索了均相成核。然而，不完全乳化和分散液滴的非单峰尺寸分布往往会导致非均相成核。这反过来会影响冷冻浓缩溶液的分布和固体冰/硫酸铵混合物的浓度，从而影响在低于冰点温度时的相行为。例如，在183K时，钙钛矿的形成关键取决于液滴是不均匀冻结还是均匀冻结。因此，乳化技术可以是一项非常强大的技术，但必须确保乳化完成，即液滴在15微米附近达到单峰尺寸分布。此外，基质本身的相分离或从空气中吸收水分可能会阻碍实验。(C)2016年作者(S)。除另有说明外，所有文章内容均受知识共享署名(CC BY)许可证(http://creativecommons.org/licenses/by/4.0/).的许可
Here we investigate the freezing and thawing properties of aqueous solutions in oil emulsions, with a particular focus on investigating the influence of the oil and surfactant and the stirring time of the emulsion. Specifically, we employ optical cryomicroscopy in combination with differential scanning calorimetry to study the phase behavior of emulsified 25 wt. % ammonium sulfate droplets in the temperature range down to 93 K. We conclude that the nucleation temperature does not vary with oil-surfactant combination, that is, homogeneous nucleation is probed. However, incomplete emulsification and non-unimodal size distribution of dispersed droplets very often result in heterogeneous nucleation. This in turn affects the distribution of freeze-concentrated solution and the concentration of the solid ice/ammonium sulfate mixture and, thus, the phase behavior at sub-freezing temperatures. For instance, the formation of letovicite at 183 K critically depends on whether the droplets have frozen heterogeneously or homogeneously. Hence, the emulsification technique can be a very strong technique, but it must be ensured that emulsification is complete, i.e., a unimodal size distribution of droplets near 15 mu m has been reached. Furthermore, phase separation within the matrix itself or uptake of water from the air may impede the experiments. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).