Characteristics of air entrainment during dynamic wetting failure along a planar substrate
Characteristics of air entrainment during dynamic wetting failure along a planar substrate
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沿平面基材动态润湿失效过程中夹带空气的特征
DOI：
10.1017/jfm.2014.110
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发表时间：
2014
影响因子：
3.7
通讯作者：
S. Sushanth Kumar
中科院分区：
文献类型：
--
作者：
Eric Vandre;Marcio S. Carvalho;S. Sushanth Kumar
摘要研究了沿着平面基片动态润湿破坏过程中，基片速度和弯月面形状与空气夹带的关系。使用高速视频，动态接触线（DCL）的行为被记录为磁带基板是通过一个浴的甘油/水溶液。空气夹带是由三角形的空气膜，从DCL延长超过一些临界基板速度。在基底和固定板之间的窄间隙内的弯月面限制被示出对于宽范围的液体粘度延迟空气夹带到更高的速度，扩展了Vandre，Carvalho和Kumar（J.Fluid Mech.，第707卷，2012年，pp. 496 - 520）。加压液体储存器控制限制间隙内的弯月面位置。研究发现，当弯月面位于静止平板上沿着的尖角附近时，液体增压进一步推迟了空气的夹带。弯月面形状记录附近的DCL表明，操作条件的影响夹带空气膜的大小，与较小的膜出现在更粘的解决方案。无论大小，空气膜变得不稳定的厚度扰动，并最终破裂，导致夹带的气泡。记录的临界速度和空气膜尺寸比较以及从流体动力学模型的动态润湿故障的预测，这表明强空气应力附近的DCL触发空气夹带的发病。
Abstract Characteristic substrate speeds and meniscus shapes associated with the onset of air entrainment are studied during dynamic wetting failure along a planar substrate. Using high-speed video, the behaviour of the dynamic contact line (DCL) is recorded as a tape substrate is drawn through a bath of a glycerol/water solution. Air entrainment is identified by triangular air films that elongate from the DCL above some critical substrate speed. Meniscus confinement within a narrow gap between the substrate and a stationary plate is shown to delay air entrainment to higher speeds for a wide range of liquid viscosities, expanding upon the findings of Vandre, Carvalho & Kumar (J. Fluid Mech., vol. 707, 2012, pp. 496–520). A pressurized liquid reservoir controls the meniscus position within the confinement gap. It is found that liquid pressurization further postpones air entrainment when the meniscus is located near a sharp corner along the stationary plate. Meniscus shapes recorded near the DCL demonstrate that operating conditions influence the size of entrained air films, with smaller films appearing in the more viscous solutions. Regardless of size, air films become unstable to thickness perturbations and ultimately rupture, leading to the entrainment of air bubbles. Recorded critical speeds and air-film sizes compare well to predictions from a hydrodynamic model for dynamic wetting failure, suggesting that strong air stresses near the DCL trigger the onset of air entrainment.