Role of Molecular Interactions on Phase Stability and Phase Behavior of a Model Nematogen-A Thermodynamic Approach

In this paper, we address the calculation of configurational interaction energy, entropy, and free energy of a liquid crystal molecule higher in the homologous series of p-n-alkyl benzoic acids (nBAC) with a heptyl group (7BAC). The atomic net charge and dipole moment at each atomic center has been evaluated using the complete neglect differential overlap (CNDO/2) method. The modified RayleighSchrodinger perturbation theory, along with multicentered-multipole expansion method, has been employed to evaluate 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 as input to calculate the thermodynamic parameters such as entropy and Helmholtz free energy of each configuration at room temperature, nematic-isotropic transition, and above transition temperature. An attempt has been made for theoretical interpretation of the role of molecular interactions on phase stability/behavior based on thermodynamic framework introduced in this paper.