Ripening of splashed 4He crystals by acoustic waves with and without gravity

By developing a refrigerator compatible with the parabolic flight of a small jet plane, 4He crystals in a superfluid were obtained in zero-gravity conditions at 0.6K.We report Ostwald ripening of these crystals in the superfluid after being splashed by acoustic waves. Ostwald ripening is a process in which smaller crystals melt and larger ones grow to minimize the overall surface energy. Under gravity on the ground, this ripening was not apparent because it stopped growing at a capillary length of about 1mm; crystals at lower positions grew to minimize the gravitational energy. Without gravity, however, Ostwald ripening was observed up to the order of 10mm, a much greater length than the 1mm due to the infinitely long capillary length, exhibiting a novel evolution of the crystal shape driven solely by the surface energy. S Online supplementary data available from stacks.iop.org/NJP/14/123023/ mmedia 1 Author to whom any correspondence should be addressed. Content from this work may be used under the terms of the Creative Commons Attribution-NonCommercialShareAlike 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New Journal of Physics 14 (2012) 123023 1367-2630/12/123023+11$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft