Dielectric relation in liquid crystals with the nematic and smectic A polymorphism

Dielectric relaxation studies are reported of several substances exhibiting the nematic (N) and smectic A (Sm A) polymorphism. From the relaxation times tau(parallel to) characterizing molecular reorientations around the short axes the activation enthalpies Delta H-parallel to for both phases were calculated. It was found that Delta H-parallel to(N) is markedly larger than Delta H-parallel to(SmA). The effect is interpreted on the basis of existing models of Sm A phase.