Rhythmic motion of colloidal particles driven by optical force

Abstract

We observed the collective motion of colloidal particles moving along a circular path in water as a model system of artificial active matter. The particles were driven by optical vortex using holographic optical tweezer. They exhibit rhythmic motion with spontaneous formation of clusters and their dissociation by hydrodynamic interaction. The hydrodynamic interaction in spatially confined system alter their rhythmic motion dramatically. For example, we found that the relative magnitude of the angular velocity for a doublet to a singlet reversed in free space and in strongly confined system. The transition of rhythmic motions was observed by varying spatial confinement.