Dynamic Dewetting: Designing and Breaking Novel Morphologies of Liquid Films

当小液滴沉积在光滑表面上时，它会在表面上扩散，直到达到平衡液滴形状或成为薄膜。这允许在基本水平上研究动态润湿过程，从而能够理解接触线运动的流体力学。这种理解在许多工业过程中非常重要，例如印刷。然而，过程通常以液体膜而不是液滴开始，并且环境或一些其他参数的变化可以引发去湿过程，即表面上的膜弹回或破碎成一个或多个液滴。初始膜状态及其从表面的去湿对于工业过程是重要的，例如用于光刻、涂漆/涂覆、印刷、热交换器等的旋涂膜。理解去湿的一个困难是，以导致理想液滴状态的受控方式启动表面上的液体膜的破裂是极其具有挑战性的。去湿通常导致液滴和水坑的混合物，使得难以研究过程的动力学或控制最终的液滴状态。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润湿非润湿表面的新方法。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）和它们的去湿动力学，以一种以前从未有过的方式进入单个液滴状态。我们调查液中液系统的粘度比的数量级对比（从液滴在空气中的液体在液体中的气泡在液体中），从而阐明接触线运动的流体力学的基本原理。我们还研究了可单独编程的膜形态到润湿图案的完全可编程阵列的组合。精细控制液体膜的能力具有从印刷到显示器的工业应用的潜力。最后，我们建立了一个新的概念电场稳定的表面局部化的二维乳液，其中的液滴或气泡的阵列可以从表面分离，并以受控的方式重新连接。

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.