Departament d'Estructura i Constituents de la Matèria, Universitat de Barcelona, Avinguda Diagonal 647, E-08028 Barcelona, Spain.
Nat Mater. 2011 May;10(5):367-71. doi: 10.1038/nmat2998. Epub 2011 Apr 10.
The controlled formation of micrometre-sized drops is of great importance to many technological applications. Here we present a wetting-based destabilization mechanism of forced microfilaments on either hydrophilic or hydrophobic stripes that leads to the periodic emission of droplets. The drop emission mechanism is triggered above the maximum critical forcing at which wetting, capillarity, viscous friction and gravity can balance to sustain a stable driven contact line. The corresponding critical filament velocity is predicted as a function of the static wetting angle, which can be tuned through the substrate behaviour, and shows a strong dependence on the filament size. This sensitivity explains the qualitative difference in the critical velocity between hydrophilic and hydrophobic stripes, and accounts for previous experimental results of splashing solids. We demonstrate that this mechanism can be used to control independently the drop size and emission period, opening the possibility of highly monodisperse and flexible drop production techniques in open microfluidic geometries.
受控制的微尺度液滴形成对于许多技术应用非常重要。在这里，我们提出了一种基于润湿的不稳定机制，即强制微丝在亲水或疏水条纹上发生变形，从而导致液滴周期性地发射。在最大临界驱动力以上，会触发液滴发射机制，此时润湿、毛细作用、粘性摩擦力和重力可以达到平衡，从而维持稳定的驱动接触线。相应的临界细丝速度可以预测为静态润湿角的函数，该润湿角可以通过基底行为进行调节，并且对细丝尺寸具有强烈的依赖性。这种敏感性解释了亲水和疏水条纹之间临界速度的定性差异，并解释了之前关于固体飞溅的实验结果。我们证明，这种机制可以独立地控制液滴尺寸和发射周期，为在开放式微流控几何形状中实现高度单分散性和灵活的液滴生产技术开辟了可能性。
