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.