Dynamics and Interactions of Colloidal Particles on Freely Suspended Smectic Films

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Freely suspended smectic films are unique liquid structures with thicknesses between a few molecular layers and a few microns, with lateral extensions up to several centimeters. They represent easily prepared models of two-dimensional (2D) fluids. In the transition from three to two dimensions, the description of the dynamics often simplifies, but there are also qualitatively new phenomena. Under certain circumstances, the dynamics in a two-dimensional liquid can be relatively complicated (see, e.g. the Stokes paradox).Depending on the mesophase, smectic films may be anisotropic (smectic C or smectic C*) or isotropic (smectic A) in the film plane. We study the motion of particles in the quasi-2D geometry of such films, and their interactions with the surrounding director field.In the previous funding period, the preparation of solid and liquid inclusions in smectic films was developed and the motion of solid beads was studied with the aid of polarized light microscopy experiments. We could test and verify the Saffman-Delbrück model for the mobility of inclusions in 2D fluids and the transition between the limiting cases of the model was observed. A technique to shoot microdroplets onto smectic films was developed, and the impact of these droplets, their incorporation into the films or the tunneling through the films were described. Coalescence prozesses of circular islands were observed and analyzed quantitatively. The findings for 2D isotropic SmA films have now been published. We will now focus on the motion in anisotropic SmC films, and investigate anisometric (shape anisotropic) particles. Two new and interesting aspects are the incorporation of the set of shear viscosities and the rotational viscosity in anisotropic 2D fluids, as well as the reorientation dynamics of rod-shaped inclusions.For both topics, there are qualitative preliminary studies, but neither the group of the applicant nor other research groups so far have obtained experimental results. We plan both quantitative experiments and numerical (FEM) simulations. They will form the basis of a systematic description of hydrodynamic processes in quasi-2D anisotropic fluids.