  Domain decay is at the heart of the so-called evaporation-condensation
Ostwald-ripening regime of phase ordering kinetics, where the growth of large
domains occurs at the expense of smaller ones, which are expected to
`evaporate'. We experimentally investigate such decay dynamics at the level of
a single spherical domain picked from one phase in coexistence and brought into
the other phase by an opto-mechanical approach, in a near-critical
phase-separated binary liquid mixture. We observe that the decay dynamics is
generally not compatible with the theoretically expected surface-tension decay
laws for conserved order parameters. Using a mean-field description, we
quantitatively explain this apparent disagreement by the gradient of solute
concentrations induced by gravity close to a critical point. Finally, we
determine the conditions for which buoyancy becomes negligible compared to
capillarity and perform dedicated experiments that retrieve the predicted
surface-tension induced decay exponent. The surface-tension driven decay
dynamics of conserved order parameter systems in the presence and the absence
of gravity, is thus established at the level of a single domain.
