When a droplet interacts with a water-repellent surface, its triple-phase contact line typically exhibits varying contact angles, which can vary from point-to-point across the surface. Consequently, measuring the contact angles along the contact line would provide a better representation of the wetting properties of the surface than a single average contact angle. However, an effective method for estimating the local contact angle along the contact line on opaque hydrophobic surfaces is currently lacking. Here we present a method that combines through-drop imaging of the wetting interface during a sliding experiment with Finite Element Modeling of the droplet to estimate contact angle values along the contact line. Using this method, the mean advancing and receding contact angles were measured on four types of hydrophobic samples with contact angles between 99 and 178.9°. The method was further used to produce detailed advancing and receding contact angle maps of surfaces with wetting patterns with an unprecedented resolution of 3 μm.

中文翻译：

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液-固界面的透过液滴成像：从沿液滴周边的接触角变化到跨表面接触角的映射

当液滴与防水表面相互作用时，其三相接触线通常表现出不同的接触角，该接触角在表面上的点与点之间可能有所不同。因此，沿着接触线测量接触角将比单个平均接触角更好地表示表面的润湿特性。然而，目前缺乏一种有效的方法来估计不透明疏水表面上沿接触线的局部接触角。在这里，我们提出了一种方法，该方法将滑动实验期间润湿界面的穿透液滴成像与液滴的有限元建模相结合，以估计沿接触线的接触角值。使用该方法，测量了接触角在 99 至 178.9° 之间的四种疏水性样品的平均前进和后退接触角。该方法进一步用于生成具有润湿图案的详细表面前进和后退接触角图，其分辨率达到前所未有的 3 μm。