Attraction and repulsion of floating particles

Abstract

2889 (1982).The horizontal force that has to be applied to floating cylinders to equilibrate the capillary force is calculated for a general geometry with cylindrical symmetry and for any wetting characteristics of the cylinders. The force on a cylinder can be related to a single parameter of each of the two menisci that contact the cylinder. It is found that the force between parallel vertical plates or parallelipipeds can be repulsive if one of the contact angles is acute and the other obtuse. The force on cylinders between fixed walls is also calculated and the results suggest that it may be possible to separate floating particles with different wetting properties by placing them between two walls with different contact angles. M. A. FORTES. Can. J. Chem. 60, 2889 (1982). On a calculC la force horizontale que doit &tre appliquee a des cylindres flottants pour Cquilibrer les forces capillaires, pour une geometric gCnCrale avec une symetrie cylindrique et pour n'importe quelle caracteristique de rnouillage des cylindres. On peut relier la force sur un cylindre a un parametre unique pour chacun des deux menisques qui sont en contact avec le cylindre. On a trouve que les forces entre les plaques verticales paralleles ou parallelCpipedes peuvent &tre repulsives si un des angles de contact est aigu et I'autre obtu. On a egalement calcule la force qui s'exerce sur le cylindre entre deux parois fixes; les resultats suggtrent qu'il est possible de separer des particules flottantes ayant des proprietes diffkrentes de mouillage en les pla~ant entre deux parois avec des angles de contact differents.[Traduit par le journal]

Particle motion in a liquid film rimming the inside of a partially filled rotating cylinder

“…The dynamic behaviour of clustering is not well characterized. Gifford & Scriven (1971) noted that 'casual observations . .…”

Micro- and nanoparticles self-assembly for virtually defect-free, adjustable monolayers

“…3), which is especially important for small (micro-and nano-) particles. For such small particles, the balance between the particles' buoyant weight (which scales as a 2 ) and vertical capillary force (which scales as a) implies that, in the absence of an electric force (which scales as a 2 ) and under equilibrium, there is negligible deformation of the interface (9)(10)(11)(12)(13)(14)(15)26). Consequently, the lateral capillary forces are too small to move micrometer-and smaller-sized particles along the interface, and thus, such small (neutral) particles, in general, do not self-assemble [although small particles can self-assemble if they become charged (26) or if they have irregular contact lines (27)].…”

“…However, the repulsive forces caused by the interparticles electrostatic interactions (Eq. 2) decay relatively faster (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) with the distance between the particles (these forces decay as r Ϫ4 ). Because the repulsive force decays faster than the attractive capillary force, there is an equilibrium distance at which the two curves intersect and the total lateral force acting on the particles is zero.…”

“…A popular mean used to assemble particles is based on the phenomenon of capillarity (3)(4)(5)(9)(10)(11)(12)(13)(14)(15). A common example of capillarity-driven self-assembly is the clustering of cereal flakes floating on the surface of milk.…”

“…A common example of capillarity-driven self-assembly is the clustering of cereal flakes floating on the surface of milk. The floating cereal particles experience attractive capillary forces, because when two such particles are close to each other, the deformed interface around them is not symmetric because the interface height between the particles is lowered owing to the interfacial tension (9)(10)(11)(12)(13)(14)(15). This lowering of the interface between the particles gives rise to lateral forces that cause them to come together.…”