John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Phys Rev Lett. 2020 Jun 26;124(25):258002. doi: 10.1103/PhysRevLett.124.258002.
When a volatile droplet is deposited on a floating swellable sheet, it becomes asymmetric, lobed and mobile. We describe and quantify this phenomena that involves nonequilibrium swelling, evaporation and motion, working together to realize a self-excitable spatially extended oscillator. Solvent penetration causes the film to swell locally and eventually buckle, changing its shape and the drop responds by moving. Simultaneously, solvent evaporation from the swollen film causes it to regain its shape once the droplet has moved away. The process repeats and leads to complex pulsatile spinning and/or sliding movements. We use a one-dimensional experiment to highlight the slow swelling of and evaporation from the film and the fast motion of the drop, a characteristic of excitable systems. Finally, we provide a phase diagram for droplet excitability as a function of drop size and film thickness and scaling laws for the motion of the droplet.
当易挥发的液滴沉积在可浮动的可溶胀薄片上时，它会变得不对称、有裂片且可移动。我们描述并量化了这一涉及非平衡溶胀、蒸发和运动的现象，这些因素共同作用实现了自激的空间扩展振荡器。溶剂渗透会导致薄膜局部膨胀，最终发生屈曲，从而改变其形状，液滴会通过移动做出响应。同时，从溶胀薄膜中蒸发溶剂会导致薄膜在液滴移动后恢复其形状。这个过程会重复，导致复杂的脉冲式旋转和/或滑动运动。我们使用一维实验突出了薄膜的缓慢溶胀和蒸发以及液滴的快速运动，这是激活动力学系统的特征。最后，我们提供了一个作为液滴尺寸和薄膜厚度函数的液滴激活动力学相图，以及液滴运动的标度律。
