Morphology transition observed in a phase separating fluid

The relation between morphology and kinetics of phase ordering in fluids is studied near a critical point (with benefit of universality) and under reduced gravity. The volume fraction {φ} of the phases governs the phase ordering. It is varied in a SF₆ sample (density 0.85% off critical) by performing thermal quenches below the coexistence curve (range: 50--2490 {μ}K). We observe for φH=(29±3)% a transition from a pattern of isolated drops (φ<φH), whose distance grows as (time)1/3, to a pattern of interconnected drops (φ>φH), with distance growing as (time)¹. The transition separates the regions where collisions of droplets, which dominate the dynamics, are due to Brownian diffusion or to hydrodynamic interactions.