Curvature Capillary Repulsion

On a curved fluid interface, microparticles interact with the curvature field in a manner akin to a charged multipole in an applied external electrostatic field. The interaction is driven by capillarity where particles move to minimize the excess area associated with the distortions that they make in the interface. Here, we present capillary curvature repulsion. We study microparticles migration on a curved host interface with zero mean curvature, which is created by pinning an oil-water interface around a micropost. We identify curvature fields in which microparticles migrate away from high curvature sites. By a combination of theory and experiment, we show how these interactions occur and their relationship to particle and post geometry. By tuning repulsion and attraction, we define sites far from bounding surfaces for particle assembly at equilibrium on interfaces, and explore collective behaviors of particles near these sites. Understanding of effects of curvature on the behavior of microparticles at the interfaces provides implications to create reconfigurable hierarchical structures.