화학공학소재연구정보센터
Molecular Crystals and Liquid Crystals, Vol.533, 92-101, 2010
Molecular Order-Disorder Phenomenon of a Nematogen: A Computational Analysis
The system chosen for the present investigation, para-azoxyanisole (4AA), exhibits a nematic-isotropic transition temperature at 408K. A computational analysis based on quantum mechanics and statistical thermodynamics has been carried out with respect to translational and orientational motions. The evaluation of net atomic charges and dipole moment at each atomic center has been carried out through the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, and the 6-exp potential function has been assumed for short-range interaction. The total interaction energy values obtained through these computations have been used as input to calculate the probability of occurrence of a particular configuration using the Maxwell-Boltzmann formula. Further, thermodynamic parameters such as Helmholtz free energy, entropy at room temperature (300K), nematic-isotropic transition temperature (408K), and above transition temperature (500K) have been computed. An attempt has been made to understand the order-disorder phenomenon exhibited by a nematogen and to develop a new and interesting model for structure-phase stability relationships at the molecular level.