We report a coalescence mechanism between the droplet and precursor liquid that is responsible for the transition between unidirectional and bidirectional propagation of droplets on heterogeneous surfaces. Through visualizing the liquid propagation dynamics at a microscopic scale, we show how the coalescence between the droplet and precursor film/filament devastates the pinning effect induced by heterogeneous topography, and in turn, results in the macroscopic breakdown of unidirectional droplet propagation. We further show the manipulation of liquid propagation dynamics with surface wettability and topography. This work advances the fundamental understanding of navigating tiny liquid droplets on-demand that finds applications in various fields, oil–water separation, water harvesting, microfluidics, printing, coatings and microfabrication, to name a few.

中文翻译：

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液滴单向和双向传播之间的聚结诱导过渡

我们报告了液滴和前体液体之间的聚结机制，该机制负责在非均质表面上液滴的单向传播和双向传播之间的过渡。通过在微观尺度上可视化液体传播动力学，我们展示了液滴与前体薄膜/细丝之间的结合如何破坏由异质形貌引起的钉扎效应，进而导致单向液滴传播的宏观破坏。我们进一步显示了具有表面润湿性和形貌的液体传播动力学的操纵。这项工作推动了按需导航微小液滴的基本理解，从而在各种领域中找到了应用，如油水分离，集水，微流体，印刷，涂层和微细加工，