The challenge when studying the impact and sliding of free-rising air bubbles on tilted surfaces is an experimental limitation in obtaining the film thickness of thin liquid film (TLF) during the bubbles’ sliding on tilted surfaces. In this work, spatiotemporal evolution in the film thickness of the moving TLF between a sliding air bubble and a tilted plate was monitored by using a two-wavelength synchronized reflection interferometry microscopy (SRIM) technique. The evolution of the film thickness was directly determined from a timed series of monochromatic interference fringes recorded simultaneously at two different wavelengths. From the film thickness profile, a shear stress map at a given time was determined at different bubble sizes and inclination angles. Results showed that the film thickness of TLFs during the bubbles’ sliding on tilted surfaces was in the range of 300–1200 nm, depending on bubble size and tilting angles. Sliding of air bubbles on tilted plates over a thin gap with a few hundred nanometers thickness yielded shear stress in the order of 10–50 Pa. Both the larger bubble size and higher tilting angles yielded a higher shear stress. Experimental results were quantitatively compared to numerical results obtained using the Reynolds lubrication theory. A good match between the two results was achieved. Numerical results suggested that a maximum shear stress exerted on a tilted plate occurred at a 25° tilting angle. This is the first time that the spatiotemporal evolution of TLF during bubbles’ sliding on tilted surfaces has been achieved, and the shear stress exerted on the tilted surface has been directly determined.

中文翻译：

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气泡在倾斜板上滑动过程中的薄液膜视图和剪切应力


研究自由上升气泡在倾斜表面上的冲击和滑动时面临的挑战是在气泡在倾斜表面上滑动期间获得薄液膜（TLF）的膜厚度的实验限制。在这项工作中，通过使用双波长同步反射干涉测量显微镜 (SRIM) 技术来监测滑动气泡和倾斜板之间移动的 TLF 薄膜厚度的时空演变。薄膜厚度的变化直接由在两个不同波长下同时记录的一系列单色干涉条纹确定。根据薄膜厚度分布，在不同的气泡尺寸和倾斜角度下确定给定时间的剪切应力图。结果表明，气泡在倾斜表面上滑动期间，TLF 的膜厚度在 300-1200 nm 范围内，具体取决于气泡尺寸和倾斜角度。气泡在倾斜板上在几百纳米厚的薄间隙上滑动，产生了 10-50 Pa 量级的剪切应力。较大的气泡尺寸和较高的倾斜角度都会产生较高的剪切应力。将实验结果与使用雷诺润滑理论获得的数值结果进行定量比较。两个结果之间取得了很好的匹配。数值结果表明，施加在倾斜板上的最大剪切应力出现在倾斜角为 25° 的位置。这是首次实现了气泡在倾斜表面滑动过程中TLF的时空演化，并直接确定了施加在倾斜表面上的剪切应力。