Molecular Dynamic Investigation of Liquid Crystals Consisting of Disc-Like Molecules

Abstract

Abstract The results of first-made molecular-dynamic investigation of liquid crystals formed by disc-like molecules are given. The proposed molecular model is based on the representation of molecules in the form of flattened ellipsoids of rotation in the centres of which spherical centres of repulsion and/or attraction are located in some cases. Besides steric factors related to the form of molecules the potential of the pair interaction takes into account anisotropy of forces of dispersive attraction. In some cases this potential also included dipole-quadrupole interaction causing the effect of cholesteric twisting. The statistic problem was solved by the molecular dynamics method, i.e. by way of solving the system of equations for the movement of particles interacting with one another, which were placed in the basic sample with periodic boundary conditions. The numbers of particles in the main sample were 168 or 256. The data obtained in the process of modeling (after the transition of the system into the equilibrium state) permitted to judge about the structure of the system (translational and orientational distribution functions, order parameters, coordinational numbers), equilibrium properties (pressure, energy, compressiblity, heat capacity, thermodynamic velocity of sound) and transport characteristics (time correlation functions, coefficients of self-diffusion). The contribution of molecular interaction energy to structure characteristics was found as well as dynamic behaviour of particles and physicochemical properties. The analysis of results obtained allowed to admit the possibility of existence in certain intervals of temperature and density of some liquid crystalline mesophases many of which have not been observed experimentally up to now. The method of molecular dynamics gave the possibility to predict many properties of such systems and to judge about the peculiarities of phase transitions between similar mesophases.