Topology changes of the interface between two immiscible liquid layers by a rotating lid.

We report a deformation phenomenon occurring at the interface between two immiscible liquids. The two liquids are in a cylindrical container and set into motion by a rotating lid positioned above the interface. The upper liquid is more viscous than the lower and the difference in densities between the liquids is fairly small. As the rotational speed of the lid (Omega) is increased in small increments, the center of the interface rises and the height increases. Depending on Omega , the topology of the interface changes drastically. The shape of the interface depends strongly on Omega and also the volume fraction of the liquids. Some dynamical behavior of the interface accompanies the changes in topology: interfacial waves, the generation of droplets, and interfacial instability.