Electrohydrodynamic Particle Structuring on a Drop Interface

We experimentally study the dynamics of colloidal particles adsorbed on a drop placed in a uniform DC electric field. The interplay of dielectrophoretic attraction and convection by the electrohydrodynamic flow gives rise to variety of particle assemblies. In weak electric fields, particles move towards the equator forming a "belt". As the field strength increases, the belt becomes unstable and breaks into a sequence of counter-rotating vortices of particles. In strong fields, the particles chain and may tip-stream from the drop poles. The diversity of particle patterns and drop shapes provides new ideas for directed assembly of particles at interfaces. The observed dynamics may also apply to other complex surfaces, such as domains on fluid bilayer membranes.