Temperature-gradient-induced thermomigration in smectic liquid crystal bubbles and freely suspended films in microgravity*

In-plane temperature gradients were applied to tethered smectic bubbles on the ISS during the OASIS mission and to thin freely-suspended smectic films during suborbital rocket flights in order to study the Marangoni effect in a 2D fluid in microgravity. Tethered bubbles of smectic A liquid crystal were inflated in a temperature-controlled chamber. An emulsion of islands subsequently generated on the bubble with an air jet was initially homogeneously distributed over the entire bubble surface. When the inflation syringe was heated, however, the islands moved away from the point of heating, with the island velocity decreasing as they migrated away from the syringe. The islands appear to be moving with the background film, not as a direct consequence of the thermal gradient. In flat films, on the other hand, in-plane temperature gradients were observed to cause two specific Marangoni effects, directed flow and convection patterns.
[1] T. Trittel, et al., Phys. Rev. Lett. 122, 234501 (2019) [2] R. Stannarius et al., New J. Phys. 21, 063033 (2019).