Directional and ratchet-like functionalized surfaces can induce liquid transport without the use of an external force. In this paper, we investigate the motion of liquid droplets near the Leidenfrost temperature on functionalized self-assembled asymmetric microstructured surfaces. The surfaces, which have angled microstructures, display unidirectional properties. The surfaces are fabricated on stainless steel through the use of a femtosecond laser-assisted process. Through this process, mound-like microstructures are formed through a combination of material ablation, fluid flow, and material redeposition. In order to achieve the asymmetry of the microstructures, the femtosecond laser is directed at an angle with respect to the sample surface. Two surfaces with microstructures angled at 45° and 10° with respect to the surface normal were fabricated. Droplet experiments were carried out with deionized water and a leveled hot plate to characterize the directional and self-propelling properties of the surfaces. It was found that the droplet motion direction is opposite of that for a surface with conventional ratchet microstructures reported in the literature. The new finding could not be explained by the widely accepted mechanism of asymmetric vapor flow. A new mechanism for a self-propelled droplet on asymmetric three-dimensional self-assembled microstructured surfaces is proposed.

中文翻译：

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具有成角度的自组装微/纳米结构的受热表面上的自推进液滴。

方向性和棘轮状的功能化表面可以在不使用外力的情况下诱导液体传输。在本文中，我们研究了功能化的自组装非对称微结构表面上莱顿弗罗斯特温度附近液滴的运动。具有成角度的微结构的表面显示出单向特性。这些表面通过使用飞秒激光辅助工艺在不锈钢上制成。通过该过程，通过材料烧蚀，流体流动和材料再沉积的组合形成了类似丘的微结构。为了实现微结构的不对称性，飞秒激光相对于样品表面成一定角度。制作了两个具有相对于表面法线成45°和10°角的微结构的表面。用去离子水和水平加热板进行液滴实验，以表征表面的方向性和自推进性。发现液滴运动方向与文献中报道的具有常规棘轮微结构的表面的运动方向相反。新发现不能由不对称蒸气流的广泛接受的机理来解释。提出了一种在非对称三维自组装微结构表面上驱动液滴的新机制。新发现不能由不对称蒸气流的广泛接受的机理来解释。提出了一种在非对称三维自组装微结构表面上驱动液滴的新机制。新发现不能由不对称蒸气流的广泛接受的机理来解释。提出了一种在非对称三维自组装微结构表面上驱动液滴的新机制。