Role of molecular rigidity on phase organization of a smectic liquid crystal - A theoretical model

The intermolecular interaction energies between a pair of Ethyl para-azoxy benzoate (4EAB) molecules have been computed with respect to translational and orientational motions. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment components at each atomic centre. The modified Rayleigh-Schrodinger perturbation theory along with multicentred-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a '6-exp' potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300 K), smectic-isotropic transition temperature (393 K), and above transition temperature (450 K) using the Maxwell-Boltzmann formula. All possible geometrical arrangements between the molecular pairs have been considered during the different modes of interactions. An attempt has been made to understand the molecular property that influences the macroscopic behaviour and controls the equilibrium between different phases of the chosen compound. Molecular arrangements inside a bulk of materials and smectic behaviour of the compound in terms of their relative order have been discussed. Further, a theoretical model has been developed to explicate the role of molecular rigidity on flexibility of various configurations and phase organization of a smectic liquid crystal. (C) 2010 Elsevier B.V. All rights reserved.