This paper reports the behavior of water droplets on a topography-based, radial gradient on a metallic surface. The radial gradient was designed to concentrate water in the center region through the spontaneous motion and coalescence of individual droplets on the gradient pattern. In this work, parallel microchannels having a fixed width (∼25 μm) and depth (100 μm) but variable spacing were used to impart a net surface tension force to the droplet for actuation. The diameter of the radial gradient (i.e. circular test region) was approximately 18.9 mm (or, ∼0.75 inches). The surfaces were fabricated using a 355nm YVO4 laser system and then characterized using droplet injection (5 – 38 μL) and spray testing techniques. Injected droplets were observed to move spontaneously away from the hydrophobic outer ring region of the circle towards the hydrophilic center as designed by the gradient. Droplet travel distances as large as 4 mm were measured depending on the droplet volume and injection site location. In application, such a design could be useful for promoting droplet coalescence on a surface and subsequently removal by gravity through the formation of sufficiently large droplets from two or more otherwise small droplets.

本文报道了水滴在金属表面基于地形的径向梯度上的行为。径向梯度被设计为通过梯度模式上单个液滴的自发运动和聚结将水集中在中心区域。在这项工作中，使用具有固定宽度（〜25μm）和深度（100μm）但间距可变的平行微通道为液滴施加净表面张力，以进行驱动。径向梯度的直径（即圆形测试区域）约为18.9毫米（约0.75英寸）。使用355nm YVO4激光系统制造表面，然后使用液滴注入（5 – 38μL）和喷雾测试技术进行表征。观察到注射的液滴自发地从圆的疏水性外环区域移向亲水性中心，如渐变所设计的那样。根据液滴的体积和注射部位的位置，测量到的液滴行进距离可达4毫米。在应用中，这样的设计对于促进液滴在表面上的聚结以及随后通过重力作用从两个或更多个否则小的液滴的形成中形成足够大的液滴而有用。