Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature
Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature
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DOI：
10.1073/pnas.1222196110
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发表时间：
2013-06-04
影响因子：
11.1
通讯作者：
van der Gucht, Jasper
中科院分区：
文献类型：
--
作者：
Ershov, Dmitry;Sprakel, Joris;van der Gucht, Jasper
漂浮在液体界面上的物体，例如漂浮在一碗牛奶中的早餐麦片或软饮料表面的气泡，由于毛细管吸引力而聚集在一起。这种吸引力是由于重力导致液体界面变形而产生的。这些变形会导致表面积过大，如果颗粒靠得更近，表面积就会减少。然而，对于微米尺寸的胶体，重力太小而无法产生显着的界面变形，因此平坦界面处球形胶体之间的毛细管力可以忽略不计。在这里，我们表明，当限制液体界面具有有限曲率且各向异性时，情况会有所不同。在这种情况下，只有当界面发生变形时，才能满足沿三相接触线接触角恒定的条件。我们提出的实验和数值计算证明了这如何导致颗粒之间的四极毛细管相互作用，从而组织成规则的方形晶格。我们证明，无论液体界面的确切形状如何，控制各向异性相互作用的强度都可以仅通过偏曲率来重新调整。我们的结果表明，通过调整界面曲率，可以很容易地在各向同性胶体之间诱导各向异性相互作用。
Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together as a result of capillary attraction. This attraction arises from deformation of the liquid interface due to gravitational forces; these deformations cause excess surface area that can be reduced if the particles move closer together. For micrometer-sized colloids, however, the gravitational force is too small to produce significant interfacial deformations, so capillary forces between spherical colloids at a flat interface are negligible. Here, we show that this is different when the confining liquid interface has a finite curvature that is also anisotropic. In that case, the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature.