Spreading of a drop of neutrally buoyant suspension

The spreading of suspension drops on a flat surface is studied using mixtures of liquid and density-matched particles. As expected from an energy balance model, the spreading factor is reduced with increasing particle volume fraction. This decrease is quantitatively understood through an effective viscosity coefficient. However, for large drop Reynolds number, the particles are not uniformly distributed into a spread drop but form an annulus. For higher impact velocities, a particle-induced break-up of the drop is observed.