When a water drop impinges on a flat superhydrophobic surface, it bounces off the surface after certain dwelling time, which is determined by Rayleigh inertia-capillary timescale. Recent works have demonstrated that this dwelling time (i.e., contact time) is modified on curved superhydrophobic surfaces, as the drop asymmetrically spreads over the surface. However, the contact time on the curved surfaces still remains poorly understood, while no successful physical model for the contact time has been proposed. Here, we propose that the asymmetric spreading on the curved surface is driven by either Coanda effect or inertia depending on the ratio of the drop diameter to the curvature diameter. Then, based on scaling analysis, we develop the contact time model that successfully predicts the contact time measured under a wide range of experiment conditions such as different impact velocities and curvature diameters. We believe that our results illuminate the underlying mechanism for the asymmetric spreading over the curved surface, while the proposed contact time model can be utilized for the design of superhydrophobic surfaces for various thermal applications, where the thermal exchange between the surface and the water drop occurs via a direct physical contact.

中文翻译：

---

弯曲的超疏水表面上的接触时间

当水滴撞击在平坦的超疏水表面上时，在一定的停留时间后会从表面反弹，这由瑞利惯性毛细管时间标度确定。最近的工作表明，由于液滴非对称分布在整个超疏水表面上，因此该停留时间（即接触时间）有所改变。然而，在曲面上的接触时间仍然知之甚少，而尚未提出成功的接触时间物理模型。在此，我们提出，取决于墨滴直径与曲率直径的比率，通过柯恩达效应或惯性来驱动曲面上的不对称扩展。然后，基于缩放分析，我们开发了接触时间模型，该模型成功预测了在各种实验条件（例如不同的冲击速度和曲率直径）下测得的接触时间。我们相信我们的结果阐明了曲面上不对称扩散的潜在机理，而建议的接触时间模型可用于设计各种疏水性应用的超疏水性表面，其中表面和水滴之间会发生热交换通过直接的物理接触。