Viscoplastic water entry

The impact of viscoplastic droplets on a free surface of water is studied. The droplet undergoes an elasto-plastic deformation at the early stages of water entry. At large time, the yield stress dominates; therefore, the droplet solidifies and reaches an equilibrium shape. Depending on the impact velocity and the rheology of the droplet, the final morphologies vary from pear-shaped to capsules that contain bubbles. We perform an analysis of the orders of magnitude of the forces and introduce the relevant dimensionless groups. Furthermore, we categorize the final shapes in a phase diagram and analyse their geometrical properties. The process presents a method of making non-spherical beads and capsules with tunable shapes and provides information on the general problem of the impact of highly deformable objects on a liquid surface.