Visualization of a solidification process in microgravity

Using a polarization microscopy and interferometry, we have visualized the process of the advancing interface and the adjacent region of the fluid during unidirectional solidification on a sounding rocket, and compared it with that on the ground. Liquid-crystal material was used, and the phase transitions of both isotropic-nematic and nematic-solid were investigated. On the isotropic-nematic interface, some wavy patterns were observed and the existence of different mechanisms for each gravity level was identified. In front of the nematic-solid interface, microconvection, which was recognized on the ground, disappeared under the microgravity condition. We discuss the effect of gravity on thermal transport and phase transition using a liquid-crystal material as a unique model material.