John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Institute of Materials Research and Engineering, 2 Fusionopolis Way, Singapore 138634, Singapore.
Phys Rev Lett. 2018 Jun 15;120(24):244503. doi: 10.1103/PhysRevLett.120.244503.
There are currently three main classes of liquid-repellent surfaces: micro- or nanostructured superhydrophobic surfaces, flat surfaces grafted with "liquidlike" polymer brushes, and lubricated surfaces. Despite recent progress, the mechanistic explanation for the differences in droplet behavior on such surfaces is still under debate. Here, we measure the dissipative force acting on a droplet moving on representatives of these surfaces at different velocities U=0.01-1 mm/s using a cantilever force sensor with submicronewton accuracy and correlate it to the contact line dynamics observed using optical interferometry at high spatial (micron) and temporal (<0.1 s) resolutions. We find that the dissipative force-due to very different physical mechanisms at the contact line-is independent of velocity on superhydrophobic surfaces but depends nonlinearly on velocity for flat and lubricated surfaces. The techniques and insights presented here will inform future work on liquid-repellent surfaces and enable their rational design.
目前，有三种主要的疏液表面：微纳结构化的超疏水表面、接枝了“类液态”聚合物刷的平面表面和润滑表面。尽管最近取得了进展，但对于液滴在这些表面上的行为差异的机械解释仍存在争议。在这里，我们使用具有亚毫牛精度的悬臂力传感器测量了以不同速度 U=0.01-1 毫米/秒移动的液滴在这些表面的代表物上的耗散力，并将其与使用高空间（微米）和时间（<0.1 秒）分辨率的光学干涉测量观察到的接触线动力学相关联。我们发现，耗散力——由于接触线处的物理机制非常不同——在超疏水表面上与速度无关，但在平面和润滑表面上与速度呈非线性关系。这里提出的技术和见解将为疏液表面的未来工作提供信息，并能够实现其合理设计。
