Computer simulations on structure of liquid crystal mixtures

Liquid crystals, with their interesting optical properties, have an important place in electronic devices such as displays. There are many studies using continuum theory, but many open questions can be answered only in the framework of a microscopic description. Simulations on the molecular level are very promising, but require large amounts of CPU time, even on modern, powerful hardware. The Gay-Berne Potential is applied frequently, providing a good compromise between realism and easy parametrisation. Results of Monte Carlo simulations on 512 particles are given. Systems with elongation 1.5, 2, 2.5, 3, 3.5, 4 and 5 were carefully compressed at temperature range from 0.5 up to 1.5. Short molecules do not have any orientational order even at high density, while with increasing elongation the ordering tendency becomes much more pronounced. We have studied equimolar mixtures of lengths 3.0 and 1.5 by Monte Carlo simulations on 1000 particles. We report investigations on the influence of the density and the temperature on the structure of a mixture. The work centers on the 'sandwich' structures made up by alternating layers of longer particles forming a smectic phase and shorter molecules that retain an isotropic arrangement even at high pressure. The structures were analyzed by order parameter, pressure, energy and correlation functions in order to deduce the transitions between the isotropic, nematic and smectic phase. Also, direct visualization of structures was used to observe the ordering process. (author)