Liquid-vapor phase separation in a thermocapillary force field

We study the growth of gas bubbles surrounded by liquid during the phase separation of a pure CO2 sample quenched from one-phase to two-phase region of the phase diagram by rapid cooling in microgravity. The vicinity of the critical point ensures slowing-down of the growth process. The bubble growth by coalescence is modified by local laser heating. It induces a thermocapillary (Marangoni) effect that attracts the bubbles towards the center of the beam. At the beginning of the phase separation, a bubble is trapped there and captures the surrounding bubbles. The growth exponent for the central bubble radius is close to 0.5, while that for the other bubbles is 1/3. We present a theoretical model that explains the experimental data and justifies that the temperature can vary along the gas-liquid interface in a pure fluid during its phase separation.