  The morphological paths towards equilibrium droplets during the late stages
of the dewetting process of a liquid film from a liquid substrate is
investigated experimentally and theoretically. As liquids, short chained
polystyrene (PS) and polymethyl-methacrylate (PMMA) are used, which can be
considered as Newontian liquids well above their glass transition temperatures.
Careful imaging of the PS/air interface of the droplets during equilibration by
\emph{in situ} scanning force microscopy and the PS/PMMA interface after
removal of the PS droplets reveal a surprisingly deep penetration of the PS
droplets into the PMMA layer. Droplets of sufficiently small volumes develop
the typical lens shape and were used to extract the ratio of the PS/air and
PS/PMMA surface tensions and the contact angles by comparison to theoretical
exact equilibrium solutions of the liquid/liquid system. Using these results in
our dynamical thin-film model we find that before the droplets reach their
equilibrium they undergo several intermediate stages each with a well-defined
signature in shape. Moreover, the intermediate droplet shapes are independent
of the details of the initial configuration, while the time scale they are
reached depend strongly on the droplet volume. This is shown by the numerical
solutions of the thin-film model and demonstrated by quantitative comparison to
experimental results.
