DEPENDENCE OF THE SMECTIC C-ASTERISK LAYER REORIENTATION ON LIQUID-CRYSTALLINE POLYMORPHISM

An experimental study of the dynamic behaviour of the smectic layer re orientation under application of asymmetric electric fields is present ed for tao homologous series. One of the series (Dn) exhibits a changi ng phase sequence from N-SmC* over N*-TGBA*-SmC* to SmA*-SmC* for inc reasing alkoxy chain length while for the second series (Mn) the N'-S mC transition is observed for all homologous under investigation. It is shown that the layer reorientation times for a variation of electri c held asymmetry and field amplitude as well as temperature strongly i ncrease as soon as the occurrence of a smectic A phase is observed (D n series), while they are basically equal if only homologous with the same phase sequence are considered (Mn series). This behaviour is rela ted to the temperature dependence of the director tilt angle in the vi cinity of the transition to the high temperature phase (order of the p hase transition).