Abstract
Abstract Results of dielectric studies of the low frequency relaxation process in several substances exhibiting nematic -smectic C polymorphism are presented. They are compared with the data obtained re-cently for substances with nematic-smectic A and nematic-smectic B phase sequences. It was found that the rate of molecular reorientation around the short axes does not change at the transition between the nematic and a liquid-like smectic phase (Sm A, Sm C), whereas it is considerably retarded at that of the nematic-solid-like smectic (Sm B) phase. However, the activation barrier for this motion is markedly lower in the orthogonal smectics (Sm A, Sm B) than in the nematic and Sm C phases. The analysis of numerous experimental data on the activation enthalpy in the nematic phase shows that the Arrhenius equation conforms better with results than the Diogo-Martins approach, if the nematic range exceeds 10 K.
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