Preliminary results of the sounding rocket experiment on wetting and coalescence prevention by Marangoni effect

Abstract This paper deals with the microgravity experiment on droplets, wetting and coalescence prevention, performed on the MAXUS 5 sounding rocket launched in April 2003 from the base ESRANGE located in Kiruna—Sweden. The aim of the experiment was to study wetting and coalescence prevention phenomena, induced by thermal Marangoni flows in drops bounded by a non isothermal immiscible liquid matrix. A failure in the on-board procedure occurred just after lift off, so the automatic experimental sequence did not start, but PI's switched to the manual mode and managed to run the experiment by telescience operative mode directly from Naples. A hemispherical drop of silicone oil was formed under microgravity conditions in a matrix of Fluorinert. The drop was anchored to a moving metallic disk ( 10 mm diameter) held at controlled temperature. A temperature gradient was initially established in the liquid matrix controlling the temperature of a fixed plate. During the experiment, a thin liquid film (about 100 μm thick) could be observed at sufficiently large temperature difference between the moving drop and the fixed disk (wetting prevention). The decreasing of the film thickness, as expected, was detected when the thermal gradient was reduced until wetting occurred at a “critical” temperature difference. A similar behaviour was observed during the non-coalescence study (coalescence prevention). For the different conditions investigated, the Marangoni flows in the meridian plane of the drop were detected by two CCD cameras (with different fields of view) looking at the tracers particles illuminated by an orthogonal thin laser light sheet. The paper reports the preliminary results of the microgravity experiment and a number of numerical simulations aimed at explaining and correlating the experimental findings.