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

实验研究了异丁酸（IBA）-水二元混合物层中的相分离行为，该混合物层厚度为3 mm，夹在两块蓝宝石玻璃之间，并受到垂直温度梯度的作用，使下层热端温度T B b高于临界温度T c，上层冷端温度T t低于临界温度T t。得出以下结论：1.该图案的特征在于包括一个液滴的多边形单元，类似于Assenheimer，Khaykovich和Steinberg（1994）观察到的那些，其层比目前的层薄，形成在跨层的温度梯度的有限区域中，尽管图案最终消失。相分离液滴的生长速率随温度梯度ΔT/d的增大而增大，特别是当温度梯度超过1.7K/mm时，生长速率迅速增大，并且随着温度梯度τ（=（T_tT_c）/T_c）的增大而增大。液滴消失率也观察到这些趋势。3.包括一个液滴的多边形蜂窝图案的形成归因于沿着液滴表面的热毛细运动，即，Marangoni对流。相分离液滴的生长被浓度驱动的层内瑞利对流所促进.相分离的液滴的消光通过沿液滴表面沿着的热毛细运动而增强。

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.