Dielectric studies of smectogenic dioxane mixtures revealing a nematic gap

The results of dielectric studies of two bi-component mixtures of well separated members (fourth and twelfth) of the series of 5-n-alkyl-2-(4-isothiocyanatophenyl)-1,3-dioxanes (nDBTs) are presented. Pure nDBTs exhibit the smectic A phase only, whereas the mixtures of well separated members of the series create a nematic gap. It was found that molecular rotations around the short axes are hindered by a lower activation barrier in the smectic A than in the nematic phase of the mixture, similarly to the situation for many pure substances with the same phase sequence. In the case of the lame concentration of the longer component, a crystalline phase is coated in which the short component performs uniaxial rotations in cages formed by the long molecules of the second component.