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Hydrodynamics in quasi 2D liquid crystal films - lattice structures, coalescence & coarsening -

ORAL

Abstract

Hydrodynamic phenomena in thin films play a crucial role in biological systems, in nature and modern technology. Various experimental and theoretical studies explored the motion of objects in two dimensional films [1,2], the merging behavior of objects in different systems [3,4] and the structural change of emulsions during long-term observations [5].

Here, we demonstrate and describe different phenomena dealing with isotropic droplets and smectic islands (flat circular regions) in thin quasi 2D smectic films onboard the International Space Station (ISS). We investigated the arrangement of liquid droplets in lattice-like structures and their direct interactions, including 3D droplet coalescence in these quasi 2D system [6-8]. We developed new models for the lattice structures and compared our results for the droplet coalescence with existing models for liquid lens coalescence on liquid and solid surfaces.

Additionally we analyzed the coarsening dynamics of ensembles of flat circular regions thicker than the background film – so-called smectic islands - that is based on direct island coalescence or the exchange of material through the background film (Ostwald ripening).

Since coarsening is an important phenomenon concerning the stability of liquid emulsions or the structure of foams, we compared our results with other systems and analyzed the dominant process for the 2D coarsening dynamics.

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Publication: [1] A. Eremin et al., Two-dimensional Microrheology of Freely Suspended Liquid Crystal Films, Phys. Rev. Lett. 107, 268301 (2011) <br>[2] T. Trittel., Marangoni Flow in Freely Suspended Liquid Films, Phys. Rev. Lett. 122, 234501 (2019) <br>[3] J. D. Paulsen et al., Coalescence of bubbles and drops in an outer fluid, Nat. Commun. 5, 3182 (2014)<br>[4] N. S. Shuravin et al., Coalescence of viscous two-dimensional smectic islands, Phys. Rev. E 99, 062702 (2019)<br>[5] A. Kumar et al., Slow coarsening in unstable liquid films under gravity on a disordered substrate, Phys. Rev. E 101, 042801 (2020) <br>[6] C. Klopp et al., Structure and dynamics of a two-dimensional colloid of liquid droplets, Soft Matter 15, 8156 (2019) <br>[7] C. Klopp et al., Self similarity of liquid droplet coalescence in a quasi-2D free-standing liquid-crystal film, Soft Matter 16, 4607 (2020)<br>[8] C. Klopp et al., On Droplet Coalescence in Quasi-Two-Dimensional Fluids, Langmuir 36, 10615-10621 (2020)

Presenters

  • Christoph Klopp

    Institut of experimental physics

Authors

  • Christoph Klopp

    Institut of experimental physics