Using acoustic levitation, we experimentally investigate the collective dynamics of glass microspheres inside rotating, evaporating drops. The levitated drops can rotate easily at rates up to 30 Hz through feedback with the acoustic field. We find that microparticles exhibit distinct self-assembly dynamics, from 'bands' along the equator of the axis of rotation to 'sea ice' accumulated at the north and south poles, to 'conveyor belts' of particles transported along the drop surface. To further understand these phenomena, we perform numerical simulations of particles in a rotating fluid with centrifugal force, Coriolis force, gravity, buoyancy, Stokes drag, and hydrostatic force due to centrifugal pressure gradient. Simulation results show that different dynamics of microspheres are determined by the angle between gravity and angular velocity, and the density difference between microparticles and water.
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