KINETICS OF PHASE-SEPARATION UNDER A CONCENTRATION GRADIENT

The kinetics of phase separation is investigated in a binary mixture (methanol & partially deuterated cyclohexane) submitted to a gradient of concentration (concentration is the order parameter, OP). Density matching of the phases enables gravity effects to be negligible over long times. It appears that both the morphology and the growth law of the-domains are strongly connected to the value of the OP. Only two growth laws are identified (L(m) similar to t or L(m) similar to t(1/3)). At long times, a Rayleigh-Tyalor instability can be observed. This method is applied to the determination of the coexistence curve of complex systems, like microemulsions, or to simple fluids (CO2) submitted to a gravitational field. We also report the preliminary results of a similar phenomenon, the nucleation and growth of water droplets on a substrate (dew) with a gradient of wetting properties.