Rieser Jennifer M, Arratia P E, Yodh A G, Gollub J P, Durian D J
Department of Physics and Astronomy and ‡Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
Langmuir. 2015 Mar 3;31(8):2421-9. doi: 10.1021/la5046139. Epub 2015 Feb 16.
Deformation of a fluid interface caused by the presence of objects at the interface can lead to large lateral forces between objects. We explore these fluid-mediated attractive force between partially submerged vertical cylinders. Forces are experimentally measured by slowly separating cylinder pairs and cylinder triplets after capillary rise is initially established for cylinders in contact. For cylinder pairs, numerical computations and a theoretical model are found to be in good agreement with measurements. The model provides insight into the relative importance of the contributions to the total force. For small separations, the lateral force is dominated by the fluid pressure acting over the wetted cylinder surfaces. At large separations, the surface tension acting along the contact line dominates the lateral force. A crossover between the two regimes occurs at a separation of around half of a capillary length. The experimentally measured forces between cylinder triplets are also in good agreement with numerical computations, and we show that pairwise contributions account for nearly all of the attractive force between triplets. For cylinders with an equilibrium capillary rise height greater than the height of the cylinder, we find that the attractive force depends on the height of the cylinders above the submersion level, which provides a means to create precisely controlled tunable cohesive forces between objects deforming a fluid interface.
界面处物体的存在导致流体界面变形，这会在物体之间产生较大的侧向力。我们研究了部分浸没的垂直圆柱体之间这种由流体介导的吸引力。通过在最初建立接触圆柱体的毛细上升后缓慢分离圆柱体对和圆柱体三元组来实验测量力。对于圆柱体对，发现数值计算和理论模型与测量结果吻合良好。该模型深入了解了对总力贡献的相对重要性。对于小间距，侧向力主要由作用在被浸湿圆柱体表面的流体压力主导。在大间距时，沿接触线作用的表面张力主导侧向力。两种状态之间的转变发生在大约半个毛细长度的间距处。实验测量的圆柱体三元组之间的力也与数值计算吻合良好，并且我们表明成对贡献几乎占三元组之间吸引力的全部。对于平衡毛细上升高度大于圆柱体高度的圆柱体，我们发现吸引力取决于圆柱体在浸没水平之上的高度，这提供了一种在使流体界面变形的物体之间创建精确可控的可调内聚力的方法。
