KINETICS AND MORPHOLOGY OF PHASE-SEPARATION IN FLUIDS - THE ROLE OF DROPLET COALESCENCE

We aim to relate the kinetics of phase ordering to the morphology of d omains pattern. We consider the late stages of phase transition where coarsening is coalescence-limited, in the vicinity of a liquid-liquid or gas-liquid critical points so as to benefit from its universality f eatures. The volume fraction of the phases [Phi = vapor/(liquid plus v apor)] is varied by performing thermal quenches below the phase coexis ting curve. Gravity effects are suppressed by carrying out experiments under reduced gravity and/or with density-matched binary liquids. We observe for the particular volume fraction Phi(H) = 32+/-3% a sharp tr ansition between slow growth (lengthscale similar to time(1/3), drop p attern, nose coalescence) and fast growth (lengthscale similar to time , interconnected pattern, dimple coalescence). We show from numerical and scaling analyses that a threshold value Phi(H) approximate to 30% naturally comes out from the interplay between Brownian diffusion and hydrodynamics interactions.