OASIS - Smectic Films under Microgravitation

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As part of the OASIS experiment (Observation and Analysis of Smectic Islands in Space) [1], smectic films were examined under microgravity on the ISS in cooperation with international partners. The ISS experiments took place from July 2015 to March 2016. They provided unique data on a large scale and in high quality, which are available to the cooperation partners since 2017. These data are cooperatively evaluated.The experiments included the observation of inclusions in quasi-two-dimensional (2D) liquids, the characterization of their interactions, the investigation of the spontaneous formation of ordered structures and thermocapillary experiments. Smectic films in spherical geometry (bubbles) were automatically generated in weightlessness, and inclusions in the form of islands(Layers of additional molecular layers) and drops (lenticular liquid inclusions) were prepared.Microgravity (µg) is indispensable to prevent sedimentation of the objects on the spherical bubble surface in the gravitational field. On the local scale of the observed objects, curvature is negligible. The hydrodynamic processes in the film plane were observed in long-term experiments with optical cameras. Interesting phenomena that require further investigation include the interactions of inclusions, including their merging, as well as the long-term stability of the collective structures they form.The evaluation of the data from the ISS flight, which has been very successful so far, is to be continued and supplemented by experiments under normal gravity. The primary goals are the investigation of the self-organization of drops in thin films, the dynamics of the merging of drops in the isotropic and the nematic phases, as well as the analysis and modeling of aging of two-dimensionalemulsions (Ostwald ripening).Further µg experiments with a shorter time window were carried out on parabolic flights. We investigated free-floating closed smectic films. The shape dynamics of such objects represent an intermediate case between the behavior of vesicles and soap bubbles. On short time scales, the films have a vanishing effective surface tension like vesicles. They form unique wrinkling structures that are otherwise only observable in very viscous or solid films. The aims of the investigations planned here are the characterization of such wrinkling and their modeling to derive fundamental knowledge about the shape dynamics of thin liquid films, and access to so far hardly investigated material parameters of smectic phases such as the flexibility of smectic layers. Another parabolic flight is planned.