Thermal and Fluid Transport Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Patna, Bihar 801103, India.
Langmuir. 2017 May 16;33(19):4854-4862. doi: 10.1021/acs.langmuir.7b00559. Epub 2017 May 4.
Interaction of liquids with surfaces is ubiquitous in our physical environment as well as many engineering applications. Recent advances on this topic have not only provided us with valuable insight into nature's design, but also enabled improved fluidic manipulation for liquid-based printing applications such as biomicroarrays for protein and DNA sequencing, multicolor polymer-based LED displays, inkjet printing, and solder droplet printing, among others. For example, droplet contact lines, which are typically circular on a smooth and homogeneous surface, when deposited on a microdecorated surface may take various common polygonal shapes such as squares, rectangles, hexagons, octagons and dodecagons. These polygonal contact line shapes are highly stable due to the local energy barriers associated with the anisotropy in depinning contact angles. In addition to the knowledge of the eventual contact line shapes, liquid-based printing applications would require accurate prediction of temporal evolution of contact line on these surfaces. In this work, we model and validate the evolution of droplets on microdecorated surfaces with microgoniometry experiments reported in the literature. We show that various metastable contact line shapes are formed in-between the well-known stable polygonal contact line shapes usually observed in experiments. We elucidate that the movement of the contact line between adjacent micropillars can primarily be categorized as primary zipping and transition zipping. Primary zipping occurs when the contact line moves radially outward to the next row of pillars, often resulting in the formation of a metastable contact line shape. Conversely, metastable droplet attains stable polygonal contact line shape via transition zipping wherein the contact line advances sideways. We believe that the current simulation approach can be effectively utilized for designing optimized textured surfaces for applications where control over liquid supply via surface design is required.
液体与表面的相互作用在我们的物理环境以及许多工程应用中无处不在。这一主题的最新进展不仅为我们提供了对自然设计的宝贵见解，而且还能够实现基于液体的打印应用的更好的流体控制，例如用于蛋白质和 DNA 测序的生物微阵列、多色聚合物基 LED 显示器、喷墨打印和焊锡滴打印等。例如，在光滑且均匀的表面上，液滴接触线通常呈圆形，而当沉积在微装饰表面上时，接触线可能会呈现各种常见的多边形形状，如正方形、长方形、六边形、八边形和十二边形。由于与去钉接触角各向异性相关的局部能量障碍，这些多边形接触线形状非常稳定。除了最终接触线形状的知识外，基于液体的打印应用还需要准确预测这些表面上接触线的时间演化。在这项工作中，我们使用文献中报道的微几何实验来模拟和验证微装饰表面上液滴的演化。我们表明，在通常在实验中观察到的知名稳定多边形接触线形状之间，会形成各种亚稳态接触线形状。我们阐明，相邻微柱之间的接触线的运动主要可以分为主要的拉链运动和过渡的拉链运动。当接触线径向向外移动到下一排支柱时，通常会发生主要的拉链运动，从而导致亚稳态接触线形状的形成。相反，通过过渡的拉链运动，亚稳态液滴会获得稳定的多边形接触线形状，其中接触线侧向前进。我们相信，当前的模拟方法可以有效地用于设计需要通过表面设计来控制液体供应的优化纹理表面。
