Comparative X-ray and Dielectric Studies on Some Structurally Related Smectogenic Compounds

Abstract

In continuation of our earlier work on smectogenic compounds exhibiting large bilayer spacings, we report in this paper a comparative study of several compounds with lateral methyl or methoxy substituent. Some of the compounds do not have any strongly polar end groups while others have a cyano end group. The dielectric (both static and relaxation studies up to 13 M E ) and X-ray investigations on these compounds enable us to elucidate the physical mechanisms responsible for the observed differences in the properties of the compounds. We also discuss the possible origin of the often observed reduction of the activation energy corresponding to the c,, -relaxation in the smectic A phase compared to that in the nematic phase.

X‐ray studies of the layer thickness in smectic phases

“…It seems justified to conclude that the thermal expansivity shows a small anisotropy which is more pronounced for the SmA d phase due to the competing effects mentioned already. This supports the suggestion given by Madhusudana et al [21,22] for explaining the decrease of the activation barrier hindering the molecular rotations around the short axes in the SmA phase in relation to the N phase. These authors claimed that this is due to anisotropic packing effects: the volume expansion causes an expansion mainly within the smectic layer, whereas the layer spacing hardly varies with temperature.…”

Dielectric study of three homologous Schiff base ferroelectric liquid crystals with the variations of temperature and frequency

“…On further increasing the temperature, the loss peak value has enhanced significantly, i.e., there are a larger number of free molecules with a corresponding increment of the effective dipole moment at larger temperature. 25 This type of behavior of dielectric loss has also been reported previously. 26,43 Two representative fits of the dielectric loss curve with the HN equation are shown in Figs.…”

“…Dielectric measurements of liquid crystalline materials provide useful information about the intermolecular interactions, molecular arrangements as well as their static and dynamic properties. 25 The dielectric permittivity of liquid crystalline materials depends on the response of the LC molecule under an applied electric field. The value of dielectric permittivity depends on several parameters like rotational viscosity, conductivity, dipole moment, intermolecular interactions and motions of molecules under an external field.…”