Phase-separation behavior in a binary mixture fluid layer subjected to a vertical temperature gradient

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The phase separation behaviors in a layer of isobutyric acid (IBA)-water binary mixture were experimentally investigated, where the layer with 3 mm thickness was sandwiched between two sapphire glasses and was subjected to a vertical temperature gradient by keeping the lower hot side temperature T_b above the critical temperature T_c and keeping the upper cold side one T_t below the critical one. The following conclusions were obtained.1. The patterns characterized by a polygonal cell including one droplet, similar to those observed by Assenheimer, Khaykovich & Steinberg (1994) whose layers were thinner than the present ones, are formed in a limited region of temperature gradients across the layer, although the patterns finally disappear.2. The growth rate of the phase-separated droplets increases with temperature gradient ΔT/d, especially increases rapidly beyond 1.7K/mm. In addition, the growth rate increases with increasing of τ(=(T_tT_c)/T_c). These trends were also observed for the extinction rate of the droplets.3. The formation of the polygonal cellular patterns including one droplet is attributed to the thermocapillary motion along the droplet surface, i.e., Marangoni convection.4. The growth of the phase-separated droplets is enhanced by the concentration-driven Rayleigh convection in the layer.5. The extinction of the phase-separated droplets is enhanced by the thermocapillary motion along the droplet surface.