Dynamics of spontaneous spreading with evaporation on a deep fluid layer
Dynamics of spontaneous spreading with evaporation on a deep fluid layer
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DOI：
10.1063/1.869546
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发表时间：
1998-01-01
影响因子：
4.6
通讯作者：
Troian, SM
中科院分区：
文献类型：
--
作者：
Dussaud, AD;Troian, SM
薄挥发性膜沿着较高表面张力的深流体层的表面的自发扩散为许多技术应用提供了快速和有效的传输机制。该铺展过程例如用作生物和有机Langmuir-Blodgett膜的流延中的载体机制。我们研究了不同蒸汽压和铺展系数的挥发性薄膜在深水支撑物表面上自发铺展的动力学。使用激光阴影照相术来可视化从液滴源到前缘的膜的整个表面。这种非侵入性的技术，这是高度敏感的电影表面的曲率，清楚地显示了几个移动的前沿的位置。在这项工作中，我们主要关注前沿的细节。以前的研究的非挥发性的，不混溶的薄膜上的深液层的扩展动力学表明，前缘的时间提前t（3/4）的预测层流边界层理论。我们已经发现，挥发性的，不混溶的扩散膜的前沿也随着时间t（α）的幂律而前进，其中α类似于1/2。液体蒸气压或扩散系数的差异似乎只影响前进的速度，但不影响扩散指数的值，这表明存在一个普遍的标度律。侧视激光阴影图描绘了在水中的次表面运动揭示了一个单一的拉伸对流辊的存在下的前缘的蔓延膜。这种流体循环，可能是由蒸发和随后的表面冷却的快速蔓延的膜，类似于传播瑞利-贝纳德对流辊。我们建议，这个子层的旋转流提供了额外的耗散负责降低扩展指数。(C)1998年美国物理学会。
The spontaneous spreading of a thin volatile film along the surface of a deep fluid layer of higher surface tension provides a rapid and efficient transport mechanism for many technological applications. This spreading process is used, for example, as the carrier mechanism in the casting of biological and organic Langmuir-Blodgett films. We have investigated the dynamics of spontaneously spreading volatile films of different vapor pressures and spreading coefficients advancing over the surface of a deep water support. Laser shadowgraphy was used to visualize the entire surface of the film from the droplet source to the leading edge. This noninvasive technique, which is highly sensitive to the film surface curvature, clearly displays the location of several moving fronts. In this work we focus mainly on the details of the leading edge. Previous studies of the spreading dynamics of nonvolatile, immiscible thin films on a deep liquid layer have shown that the leading edge advances in time as t(3/4) as predicted by laminar boundary layer theory. We have found that the leading edge of volatile, immiscible spreading films also advances as a power law in time, t(alpha), where alpha similar to 1/2. Differences in the liquid vapor pressure or the spreading coefficient seem only to affect the speed of advance but not the value of the spreading exponent, which suggests the presence of a universal scaling law. Sideview laser shadowgraphs depicting the subsurface motion in the water reveal the presence of a single stretched convective roll right beneath the leading edge of the spreading film. This fluid circulation, likely caused by evaporation and subsequent surface cooling of the rapidly spreading film, resembles a propagating Rayleigh-Benard convective roll. We propose that this sublayer rotational flow provides the additional dissipation responsible for the reduced spreading exponent. (C) 1998 American Institute of Physics.