Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature

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...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2013-06, Vol.110 (23), p.9220-9224
Main Authors: Ershov, Dmitry, Sprakel, Joris, Appel, Jeroen, Cohen Stuart, Martien A., van der Gucht, Jasper
Format: Article
Language:English
Subjects:
Anisotropy
arrays
attraction
Bond principal
Capillary Action
Cereals
charged particles
Colloids
Colloids - chemistry
Crystal lattices
crystals
Curvature
Deformation
Fluorescence
Gravity
liquid-liquid interfaces
Liquids
Microscopy, Confocal
Models, Chemical
Particle density
Particle energy
Particle interactions
Physical Sciences
Polystyrenes
Self assembly
Soft drinks
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Summary: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.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1222196110