Induced capillary dipoles in floating particles assemblies

Capillary-driven self-assembly is a common fabrication method that consists of placing floating particles onto a liquid-air interface. The attractive interaction between particles is due to the local deformations of the interface and is often described via so-called capillary charges. This approach holds for similar particles far from each other. When particles are close together or when they differ in size, their contact lines become tilted. By using different spherical particles, we show evidence experimentally that the capillary interaction becomes far more complex. We propose to consider induced capillary dipoles to model the menisci, therefore providing an extra attraction at short distances. This effect is enhanced for particles of different sizes such that binary self-assemblies reveal unusual local ordering.