  The partial coalescence of a droplet onto a planar liquid/liquid interface is
investigated experimentally by tuning the viscosities of both liquids. The
problem mainly depends on four dimensionless parameters: the Bond number
(gravity vs. surface tension), the Ohnesorge numbers (viscosity in both fluids
vs. surface tension), and the density relative difference. The ratio between
the daughter droplet size and the mother droplet size is investigated as a
function of these dimensionless numbers. Global quantities such as the
available surface energy of the droplet has been measured during the
coalescence. The capillary waves propagation and damping are studied in detail.
The relation between these waves and the partial coalescence is discussed.
Additional viscous mechanisms are proposed in order to explain the asymmetric
role played by both viscosities.
