Universal retraction process of a droplet shape after a large strain jump.

We evidenced a universal relaxation behavior of a droplet embedded in an immiscible fluid of the same density. After a large strain jump, the relaxation can be characterized by two related relaxation times tau(1)=4.4tau(2) independently of the viscosity ratio and of the applied strain. The change in the kinetic process is driven by the drop geometry and happens invariably when the shape of the drop is an oblate ellipsoid of revolution where the relation between the major (L) and the minor (B) axis is given by ln(LB) approximately 0.5. This universal behavior can be explained by considering the normal stress difference across the droplet interface, i.e., the curvature of the drop.