Title: Fringe around a Beet Slice: Wetting-induced Dimple in a Thin Liquid Film Show Chinese title

Title: 甜菜片周围的边缘：液体薄膜中的润湿诱导凹陷

Abstract: When a slice of beet is placed on a plate with a thin layer of beet juice, one can observe a clear fringe around the beet, where the color is more translucent than the rest of the juice. The hypotheses in literature were inconsistent and limited, which motivated us to revisit this phenomenon. Using a motorized confocal displacement sensor, we measured the temporal evolution of the liquid surface profile across the fringe. Our findings suggest that a suction flow, induced by the capillary rise of the contact line, causes a dimple - a small concave depression - to form on the liquid surface. While surface tension and gravity tends to smooth out the dimple, viscous drag acts against them if the liquid film is sufficiently thin. Our scaling analysis correctly estimates the dependence of dimple lifetime on liquid properties and film thickness. We also capture the dimple formation dynamics by numerically solving the lubrication equation with the Young-Laplace equation. This work provides a new interpretation for a common phenomenon. Show Chinese abstract

Abstract: 当一块甜菜被放在有薄层甜菜汁的盘子上时，可以观察到甜菜周围有一圈清晰的边缘，该处的颜色比其他部分更透明。 文献中的假说不一致且有限，这促使我们重新研究这一现象。 使用电动共聚焦位移传感器，我们测量了液体表面轮廓在边缘区域的时间演变。 我们的研究结果表明，由接触线毛细上升引起的吸力流动导致液体表面形成一个凹陷的小凹坑。 虽然表面张力和重力倾向于使凹坑变平，但如果液膜足够薄，粘性阻力会与之对抗。 我们的标度分析正确估计了凹坑寿命与液体性质和膜厚度的依赖关系。 我们还通过数值求解润滑方程和Young-Laplace方程捕捉了凹坑形成的动态过程。 这项工作为一种常见现象提供了新的解释。