As an air bubble translates in a microchannel, a thin film of liquid is formed on the bounding walls. In a microchannel with a rectangular cross-section, the liquid in the film leaks toward the low-pressure corners of the geometry, which leads to the appearance of local minima in the film thickness in the cross-sectional plane. In such a configuration, theory suggests that the minimum film thickness scales with Ca and Ca^4/3 depending on the distance from the nose of the bubble, where Ca = μU_b/γ is the flow capillary number based on the bubble velocity U_b, liquid viscosity μ, and surface tension γ, and Ca ≪ 1. We show that the film of a partially wetting liquid dewets on the channel wall at the sites of the local minima in the film thickness as it acquires thicknesses around and below 100 nm. Our experiments show that the distance L_w between the nose of the bubble and the initial dewetting location is a function of Ca and surface wettability. For channels of different wettability, L_w always scales proportional to Ca^α, where 1.7 < α < 2 for the range of 10^–5 < Ca < 10^–2. Moreover, L_w increases up to 10 times by enhancing the wettability of the surface at a given Ca. Our present measurements of L_w provide a design constraint on the lengths of bubbles to maintain a liquid wet channel without dry patches on the wall.

中文翻译：

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微通道中围绕气泡的液体薄膜的去湿

当气泡在微通道中平移时，在边界壁上会形成一层液体薄膜。在具有矩形横截面的微通道中，薄膜中的液体向几何形状的低压角泄漏，这导致横截面中薄膜厚度出现局部最小值。在这种结构中，理论表明，最小膜厚秤与钙和钙^4/3根据距离从气泡，鼻子，其中的Ca =μ Ü _b /γ是基于所述泡沫速度的流动毛细管数ù _b，液体粘度μ，表面张力γ和Ca≪ 1.我们发现，部分润湿液体的膜在达到最小100 nm左右的厚度时，会在通道壁的局部极小点处发生润湿。我们的实验表明，气泡鼻与初始润湿位置之间的距离L _w是Ca和表面润湿性的函数。对于不同的润湿性，的通道大号_瓦特总是缩放成比例的Ca ^α，其中，1.7 <α<2的范围为10 ^-5 <钙<10 ^-2。此外，大号_瓦特通过在给定的增强表面的润湿性增加至10倍的Ca。我们目前对L _w的测量为气泡的长度提供了设计约束，以维持液体湿通道而壁上没有干斑。