Dynamic Dewetting: Designing and Breaking Novel Morphologies of Liquid Films

当一个小液滴沉积在光滑的表面上时，它会在表面上扩散，直到它达到一个平衡的液滴形状或直到它变成一层薄膜。这使得动态润湿过程可以在基础水平上进行研究，从而可以理解接触线运动的流体力学。这种理解在许多工业过程中都很重要，比如印刷。然而，通常一个过程是从一个液体膜开始的，而不是一个液滴，环境或其他参数的变化可以启动一个脱湿过程，即表面上的膜反冲或分解成一个或多个液滴。初始薄膜状态及其从表面的脱湿对于工业过程非常重要，例如用于光刻，绘画/涂层，印刷，热交换器等的旋转涂层薄膜。理解脱湿的一个困难是，以可控的方式启动表面上液体膜的破裂，从而导致理想的液滴状态，这是极具挑战性的。脱湿通常会导致液滴和水坑的混合，这使得研究过程的动力学或控制最终液滴状态变得困难。在最近的一篇论文（Science Advances, 2016）中，我们展示了一种使用非均匀电场迫使液体湿润非湿润表面的新方法。通过淬火电场，可以启动可控的脱湿到单液滴状态。在这个项目中，我们使用电场诱导的薄膜形成来研究非自然发生的薄膜形态（例如三角形，方形和环形液滴）以及它们以一种以前从未有过的方式脱湿成单个液滴的动力学。我们研究了粘度比（从空气中的液滴到液体中的液体到液体中的气泡）的数量级对比的液中液系统，从而阐明了接触线运动的流体力学的基本原理。我们还研究了将单个可编程薄膜形态组合成完全可编程的润湿模式阵列。精细控制液体薄膜的能力在从印刷到显示的工业应用中具有潜力。最后，我们建立了电场稳定的表面局部二维乳剂的新概念，其中液滴或气泡阵列可以从表面分离并以受控的方式重新附着。

When a small droplet is deposited on a smooth surface it spreads across the surface until it reaches an equilibrium droplet shape or until it becomes a film. This allows the dynamic wetting process to be studied at a fundamental level enabling the fluid mechanics of contact line motion to be understood. This understanding is important in many industrial processes, such as printing. However, often a process starts with a liquid film, rather than a droplet, and a change of the environment or some other parameter, can initiate a process of de-wetting, i.e. the recoil or break up of a film on a surface into one or more droplets. The initial film state and its de-wetting from a surface are important for industrial processes, such as spin coated films used in lithography, painting/coatings, printing, heat exchangers, etc. One difficulty in understanding the de-wetting is that it is extremely challenging to initiate the breakup of a film of liquid on a surface in a controlled manner that leads to an ideal droplet state. Dewetting usually leads to a mixture of droplets and puddles making it difficult to study the dynamics of the process or to control the final droplet state. In a recent paper (Science Advances, 2016) we showed a new method using a non-uniform electric field to force a liquid to wet a non-wetting surface. By quenching the electric field, a controlled dewetting into a single droplet state can then be initiated.In this project, we use electric-field induced film formation to study non-naturally occurring film morphologies (e.g. triangular, square and ring droplets) and their de-wetting dynamics into single droplets in a manner, which has never previously been possible. We investigate liquid-in-liquid systems with order of magnitude contrasts in viscosity ratios (from droplets-in-air to liquids-in-liquids to bubbles-in-liquids) thereby elucidating the fundamentals of the fluid mechanics of contact line motion. We also investigate the combination of individually programmable film morphologies into fully programmable arrays of wetting patterns. An ability to finely control liquid films has potential for industrial applications from printing to displays. Finally, we establish a new concept of electric field stabilised surface-localised 2D emulsions where the arrays of droplets or bubbles can be detached from the surface and reattached in a controlled manner.