Smart Materials & Surfaces Laboratory, Faculty of Engineering and Environment, Northumbria University, Ellison Place, Newcastle upon, Tyne, NE1 8ST, UK.
Institut Universitaire de Technologie de Lannion, Rue Édouard Branly, 22300, Lannion, France.
Nat Commun. 2018 Apr 11;9(1):1380. doi: 10.1038/s41467-018-03840-6.
Droplet evaporation on solid surfaces is important in many applications including printing, micro-patterning and cooling. While seemingly simple, the configuration of evaporating droplets on solids is difficult to predict and control. This is because evaporation typically proceeds as a "stick-slip" sequence-a combination of pinning and de-pinning events dominated by static friction or "pinning", caused by microscopic surface roughness. Here we show how smooth, pinning-free, solid surfaces of non-planar topography promote a different process called snap evaporation. During snap evaporation a droplet follows a reproducible sequence of configurations, consisting of a quasi-static phase-change controlled by mass diffusion interrupted by out-of-equilibrium snaps. Snaps are triggered by bifurcations of the equilibrium droplet shape mediated by the underlying non-planar solid. Because the evolution of droplets during snap evaporation is controlled by a smooth topography, and not by surface roughness, our ideas can inspire programmable surfaces that manage liquids in heat- and mass-transfer applications.
液滴在固体表面上的蒸发在许多应用中都很重要，包括印刷、微图案和冷却。尽管蒸发看似简单，但蒸发液滴在固体表面上的形态却难以预测和控制。这是因为蒸发通常是一个“粘滑”序列——由微观表面粗糙度引起的静态摩擦力或“钉扎”主导的钉扎和去钉扎事件的组合。在这里，我们展示了如何通过非平面形貌的光滑、无钉扎、无固定表面来促进一种称为快速蒸发的不同过程。在快速蒸发过程中，液滴遵循可重复的一系列配置，包括由质量扩散控制的准静态相变化，该相变化被非平衡快速打断。快速是由底层非平面固体介导的平衡液滴形状分叉引发的。由于快速蒸发过程中液滴的演化是由光滑的形貌而不是表面粗糙度控制的，因此我们的想法可以激发可编程表面，从而在热传递和质量传递应用中管理液体。
