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 in-plane 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 non-trivial collective behaviour of domains. Various 2D structures are created as a function of the concentration and size of the inclusions. We observe the formation of chains and then 2D square lattice when the concentration of domains increases. Further increase of the domain size leads to the transition from square to hexagonal close packed structure.