Structure and dynamics of a two-dimensional colloid of liquid droplets*

Free-standing liquid crystal bubbles were prepared in microgravity on the International Space Station (ISS) in order to study the hydrodynamics of inclusions in quasi 2D fluid systems [1]. The layered structure in of smectic A and C phases allows the preparation of thin and homogeneous films. Arrays of droplets of molten film material can be formed near the clearing point when the inner layers of the film melt and the film undergoes thinning transitions. The droplets interact repulsively with each other, they spontaneously forming nearly approximately regular triangular lattices in smectic A films, with short range positional order. Local lattice cell parameters depend on droplet sizes. These structures can be considered as genuine, two-dimensional (2D) colloidal crystals. We investigate the internal dynamics in these lattices [2]. The mobility of each droplet in its six-neighbor cage is determined by the ratio of cage and droplet sizes, rather than by the droplet size as in isolated droplets.

[1] N. A. Clark et al., Adv. Space Res. 60, 737-751 (2017).
[2] C. Klopp et al., Soft Matter 15, 8156-8163 (2019).