1. In thin freely suspended films of ferroelectric and smectic C liquid crystals we have observed structures possessing longitudinal polarization (parallel to the tilt plane of the molecules). It was found that the temperature of the transition from the state with transverse polarization into the state with longitudinal polarization increases wiht decreasing film thickness. A model has been proposed relating the existence of longitudinal polarization witn nonuniform profile of the order parameter in the film which enables to calculate the temperature dependence of the longitudinal polarization and transition temperatures.

2. For the first time 2π- and π-walls were observed in thin freely suspended films of nonpolar smectic liquid crystals (Fig.1). We have observed the dissotiation of 2π-walls on two π-walls upon changing the orientation of the magnetic field with respect to the film plane (Fig.2) and dependence of the wall structure on orientation of the wall with respect to the field direction (Fig.3). Values of the two-dimensional orienational elastic constants were determined in antiferroelectric films, in smectic C and the value of longitudinal electric polarization in antiferroelectric films.

 

 

Fig. 1. Different point topological and linear defects in smectic films. π-wall in magnetic field parallel to the film plane (a), 2π-wall in the oblique field (b), two point topological defects of opposite sign, topological charges +1 and -1 (c), collapse of a 2π-wall forming a closed circular loop (d).

Fig. 2. Dependence of the 2π-wall structure on the orientation of the magnetic field with respect to the film plane. The angle α between the magnetic field and the film plane decreases from image (1) to image (3).

Fig. 3. Dependence of the 2π-wall structure on orientation of the wall with respect to the magnetic field direction. Magnetic field is perpendicular to the wall (a), field projection on the film plane is parallel to the 2π-wall (b).

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