Eur. Phys. J. E 2, 105-116
Nucleation and early stage growth in phase-separating liquid mixtures under weak time-dependent supersaturation
S. Buil - J.P. Delville - A. Ducasse
Centre de Physique Moléculaire Optique et
Hertzienne, UMR CNRS/Université No. 5798, Université Bordeaux
I, 351 Cours de la Libération F-33405 Talence cedex, France
stephanie.buil@physique.uvsq.fr
Received 1 July 1999
Abstract
In the standard description of phase separation,
quenching from an initial equilibrium state to a final metastable
state in the two-phase region is usually assumed to be
instantaneous. Such an artificial situation is nevertheless
intrinsically at variance with experiments because the quench
rate is finite due to the continuous changes in thermodynamic
parameters between the initial and final states. We
experimentally explore this issue in near-critical micellar
phases of microemulsion with induced transient grating
techniques, focusing our attention on the very early stage of
droplet growth, where the influence of the time dependence of
supersaturation is the strongest. The experiment makes use of
laser-induced concentration variations to locally quench the
mixture with two intersecting pump beams, whose interference
pattern optically traps the nucleated droplets on fringes. Due to
the slow mass diffusion kinetics of quenches in composition, the
time-resolved reflectivity of a third probe beam on the resulting
droplet grating allows us to determine the mean nucleation time
and the mean quench depth at the beginning of the decay of the
metastable state. By varying the amplitudes of the control
parameters (beam power, beam radii), we are able to characterize
the dynamic properties of nucleation onset during continuous
quenching. The results are interpreted in the light of very
simple scaling arguments. We show in particular that
for a weak linear temporal
variation of the supersaturation, where 
and 
are, respectively, the measured critical radius and nucleation
time.
PACS
64.75.+g Solubility, segregation, and mixing; phase
separation - 64.60.Qb Nucleation -
64.70.Ja Liquid-liquid transitions
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
