Stability of aqueous films between bubbles. Part 1. The effect of speed on bubble coalescence in purified water and simple electrolyte solutions.
Stability of aqueous films between bubbles. Part 1. The effect of speed on bubble coalescence in purified water and simple electrolyte solutions.
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DOI：
10.1021/la904481d
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发表时间：
2010-06-01
期刊：
影响因子：
--
通讯作者：
Horn RG
中科院分区：
文献类型：
--
作者：
Yaminsky VV;Ohnishi S;Vogler EA;Horn RG
在薄膜压力平衡中，对两个空气相之间的水膜进行了薄膜减薄实验。该薄膜不添加表面活性剂，但在一些实验中添加了简单的氯化钠电解质。最初，实验开始时在直径几毫米的圆柱形毛细管中加入相对大量的水，通过从管中心抽水，两个边界弯液面以规定的速率拉在一起。该模型模拟了两个以受控速度接近的气泡。在纯水中，结果显示了取决于接近速度的三种行为模式：在低速（<1 µm/s）下，可以形成约 100 nm 厚的纯水平坦薄膜，由于自然带电的空气/水界面之间的排斥双层相互作用，该薄膜通过分离压力无限期地稳定。数据与气泡表面-57 mV 的表面电势一致。在中等接近速度（~1 – 150 µm/s）下，由于流体动力排水效应，薄膜是瞬时稳定的，并且气泡聚结被延迟了~10 – 100 s。当接近速度大于约 150 µm/s 时，流体动力阻力似乎可以忽略不计，并且气泡合并而没有任何可测量的延迟。对这些观察结果的解释考虑了通过薄膜排水中的分离压力、表面流动性和流体动力流态进入的 DLVO 和马兰戈尼效应。特别是，有人认为，流体动力学阻力的显着降低是从粘度控制排水到惯性控制排水的转变，与增加两个气泡接近速度时从固定空气/水界面到移动空气/水界面的变化相关。开发了一个简单的模型来解释不同薄膜稳定性或聚结状态之间的界限。模型的预测与数据一致，可以解释添加电解质的影响。特别是，如先前文献所述，添加高浓度电解质会抑制近乎瞬时的聚结现象，从而有助于提高高接近速度下泡沫膜的稳定性。这项工作强调了气泡接近速度以及电解质浓度对气泡聚结的影响的重要性。
Film thinning experiments have been conducted with aqueous films between two air phases in a thin film pressure balance. The films are free of added surfactant but simple NaCl electrolyte is added in some experiments. Initially the experiments begin with a comparatively large volume of water in a cylindrical capillary tube a few mm in diameter, and by withdrawing water from the center of the tube the two bounding menisci are drawn together at a prescribed rate. This models two air bubbles approaching at a controlled speed. In pure water the results show three regimes of behavior depending on the approach speed: at slow speed (<1 µm/s) it is possible to form a flat film of pure water, ~100 nm thick, that is stabilised indefinitely by disjoining pressure due to repulsive double-layer interactions between naturally-charged air/water interfaces. The data are consistent with a surface potential of −57 mV on the bubble surfaces. At intermediate approach speed (~1 – 150 µm/s) the films are transiently stable due to hydrodynamic drainage effects, and bubble coalescence is delayed by ~10 – 100 s. At approach speeds greater than ~150 µm/s the hydrodynamic resistance appears to become negligible, and the bubbles coalesce without any measurable delay. Explanations for these observations are presented that take into account DLVO and Marangoni effects entering through disjoining pressure, surface mobility and hydrodynamic flow regimes in thin film drainage. In particular, it is argued that the dramatic reduction in hydrodynamic resistance is a transition from viscosity-controlled drainage to inertia-controlled drainage associated with a change from immobile to mobile air/water interfaces on increasing the speed of approach of two bubbles. A simple model is developed that accounts for the boundaries between different film stability or coalescence regimes. Predictions of the model are consistent with the data, and the effects of adding electrolyte can be explained. In particular, addition of electrolyte at high concentration inhibits the near-instantaneous coalescence phenomenon, thereby contributing to increased foam film stability at high approach speeds, as reported in previous literature. This work highlights the significance of bubble approach speed as well as electrolyte concentration in affecting bubble coalescence.
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影响因子：
3.4
作者：
Connor, JN;Horn, RG
通讯作者：
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影响因子：
9.9
作者：
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影响因子：
9.9
作者：
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64.8
作者：
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影响因子：
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作者：
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通讯作者：
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