1. Structure and phase transitions in thin films (2-20 molecular layers) of polar smecic liquid crystals were compared with structure and phase transitions in bulk samples. The phase transition antiferroelectric - SmC*α (structure with a short-pitch helix) - smectic A in thin films occur with formation of planar structures. The transitions are accompanied by the change of the type of polarization: transverse - longitudinal in films with an odd number of molecular layers, longitudinal - transverse in films with an even number of layers.

In thin films with bulk phase transitions antiferroelectric - SmC*FI1 (ferrielectric) - ferroelectric the temperature of the transition to the ferroelectric state increases with decreasing film thickness. In thick films(5 and more molecular layers) two branches of transitions are observed: low-temperature, related to transitions in the interior of the film and high-temperature, related with transitions at the surface.

2. Calculations of structures and phase transitions in polar liquid crystals were conducted with the aid of the discrete phenomenological Landau model of phase transitions. For the first time calculations were made with minimization of the free energy over the phase and modulus of the two-component order parameter, which enabled to obtain the temperature sequence of structures obsered in experiments. It has been shown that the ferrielectric SmC*FI1 structure is formed by change of the phase and modulus of the order parameter from layer to layer.

3. Thinning transitions (layer by layer decrease of film thickness) were investigated in feffoelectric liquid crystals. It was found that layer by layer thinning is precursed by the transition of the film into an unstable state with formation of a periodic structure of linear defects.

4. Interaction and self-organization of inclusions (particles of another liquid crystal phase, isotropic liquid) in smectic films. We observed formation of two-dimensional ordered structures from inclusions with hexagonal and square lattice (Fig. 1).

Fig. 1. Hexagonal and square structure formed by droplets in a smectic membrane.

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