Molecular Vibration Approach to Polarizabilities of Methyl Cinnamate Liquid Crystal Compounds

Abstract

A new theoretical method of evaluating polarizabilities of liquid crystals is presented and applied to the liquid crystalline compounds, namely n-alkyl-p-(4-ethoxy benzylidene amino)-α-methyl cinnamates, which exhibit smectic A and nematic phases. In the present method, vibrational frequencies are used to evaluate force constants, mean amplitude of vibration and hence bond polarizabilities. From mean polarizabilities, polarizability anisotropies and mean diamagnetic susceptibilities are also estimated. A close agreement is found between the values estimated from the present molecular vibration method and the reported data, which confirms the applicability of this method to the liquid crystals exhibiting smectic A and nematic phases. In addition, the variation of the order parameter with temperature is also studied.

Study of Molecular Polarizabilities and Orientational Order Parameter in the Nematic Phase of 6.O12O.6 and 7.O12O.7

“…From these two tables following observations can be made: the calculated values of α e , α o and (α e -α o ) using both Vuks and Neugebaur methods are marginally larger for 7.O12O.7 than those for 6.O12O.6 and the values obtained for any single compound using these two methods are almost similar. This is rather surprising as it was assumed that the molecular distribution in the Vuks model to be isotropic even in the anisotropic crystal which was applied to anisotropic liquid crystals [10], whereas, the Neugebaur model assumes anisotropy of the internal field in a crystal [13] which was applied to liquid crystals [11,12]. difference in the length of these two molecules is considered, the molecular polarizability values appears to be almost same in the nematic phase of both of these two compounds.…”

“…Anisotropy from Lippincott δ-Function Model and the Molecular Vibrational Methods The principal molecular polarizability anisotropy and the mean polarizability are evaluated for the compounds 6.O12O.6 and 7.O12O.7 using the Lippincott δ-function model [9,10] and the molecular vibration method [11]. The principal molecular polarizability components as well as mean polarizabilities for the compounds 6.O12O.6 and 7.O12O.7 using these two methods are given in Table 2.…”

Phase transitions from density and order parameter from polarisabilities in symmetric dimeric liquid crystals

“…Þ has been estimated separately using Haller approximation, [23] Lippincott δ-function model [24] and molecular vibration methods. [25] From these values, S has been calculated using Equation (1). Furthermore, S has been estimated using the refractive index data employing Vuks scaling factor method.…”

Physical Studies of Cyclohexane Derivatives

“…As the detailed theoretical procedure is given in our earlier communications [5,6] we present here only the final relation which connect longitudinal (b L ) and transverse (b) bond polarizabilities with a mean amplitude of vibration (σ1/2) where C is a constant equal to 5.24 x 10 -1 ', p is characteristic of the atom and is equal to 1, 1.2, 1.3, 1.4, and 1.5 accordingly as it belongs to 2', 3rd 4th , and 5 th or 6th row in the periodic table, n is +1 or -1 accordingly as the bond is non-hydride or hydride and r is the saturation factor. Now the average polarizability (α) of the molecule is given by where ni is the number of bonds of the type i.…”

“…In all these models temperature dependence of refractive indices and densities are used to evaluate the mean molecular polarizabilities. But in our recent communications [5,6] we have given a method namely "molecular vibration approach", in which the mean polarizabilities are evaluated using the vibrational frequency data. By employing the present method we have estimated the mean molecular polarizabilities and polarizability anisotropies.…”