When particles are suspended at the air-liquid interface, the deformation of the later implies attractive interactions. This is called the “Cheerios effect“, a reference to clumping of cereals in a breakfast bowl.
In our last paper published in Phys. Rev. E, we investigated the case of a few submillimeter magnetic beads placed at the air-liquid interface. A vertical magnetic field induces some dipole-dipole repulsive interaction which competes with capillary attraction. Equilibrium self-assembled configurations are investigated and provide clues for testing the energy potential behind the “magnetic Cheerios effect”. Unexpected phenomena such as symmetry breaking and hysteresis are observed.
N.Vandewalle et al, Phys. Rev. E 85, 041402 (2012) – PDF