Formation of two-dimensional crystal-like structures from inclusions in smectic C films

The structures formed by inclusions in smectic C (SmC) free-standing films are investigated using polarized light microscopy. The domains confined in these two-dimensional (2D) systems induce distortion of the inplane orientational order, which governs the elastic interaction between the inclusions. The balance between long-range quadrupolar attraction and short-range repulsion gives rise to a nontrivial collective behavior of domains. Various 2D structures are created as a function of the concentration and size of inclusions. We observe the formation of chains and then a 2D square lattice when the concentration of domains increases. Further increase in the domain size leads to the transition from square to hexagonal close-packed structure.