  The time-dependent structure, interfacial tension, and evaporation of an
oversaturated colloid-rich (liquid) phase in contact with an undersaturated
colloid-poor (vapor) phase of a colloidal dispersion is investigated
theoretically during the early-stage relaxation, where the interface is
relaxing towards a local equilibrium state while the bulk phases are still out
of equilibrium. Since systems of this type exhibit a clear separation of
colloidal and solvent relaxation time scales with typical times of interfacial
tension measurements in between, they can be expected to be suitable for
analogous experimental studies, too. The major finding is that, irrespective of
how much the bulk phases differ from two-phase coexistence, the interfacial
structure and the interfacial tension approach those at two-phase coexistence
during the early-stage relaxation process. This is a surprising observation
since it implies that the relaxation towards global equilibrium of the
interface is not following but preceding that of the bulk phases. Scaling forms
for the local chemical potential, the flux, and the dissipation rate exhibit
qualitatively different leading order contributions depending on whether an
equilibrium or a non-equilibrium system is considered. The degree of
non-equilibrium between the bulk phases is found to not influence the
qualitative relaxation behavior (i.e., the values of power-law exponents), but
to determine the quantitative deviation of the observed quantities from their
values at two-phase coexistence. Whereas the underlying dynamics differs
between colloidal and molecular fluids, the behavior of quantities such as the
interfacial tension approaching the equilibrium values during the early-stage
relaxation process, during which non-equilibrium conditions of the bulk phases
are not changed, can be expected to occur for both types of systems.
