SPONTANEOUSLY CREATED RING STRUCTURES IN FREESTANDING LIQUID-CRYSTAL FILMS AND THEIR DEPENDENCE ON TEMPERATURE AND MATERIAL PARAMETERS

A rotating electric held can induce a spontaneous formation of ring st ructures in free-standing ferroelectric liquid crystal films. A phase delay between the field rotation and the director movement on the smec tic cone is the reason for the ring creation. The appearance of these structures depends on the held parameters, on the material parameters of the liquid crystal compound used, and on the temperature. The tempe rature dependence of the pattern formation and of material parameters (spontaneous polarization, rotational viscosity, pitch) have been inve stigated in more detail. It could be shown that the rotational viscosi ty of the liquid crystal is the most important parameter with respect to the influence of temperature. The experimental results are compared with the theoretical interpretation of the ring formation.