COMPUTER-SIMULATION OF THE BEHAVIOR OF A SOLUTE IN A MODEL LIQUID-CRYSTALLINE SOLVENT

A method is described for modelling the behaviour of solute molecules dissolved in a model liquid crystalline solvent. The method is illustr ated for benzene as the solute, and the solvent is a collection of par ticles interacting with each other via the Gay-Berne potential. The in teraction between the benzene and each solvent particle is modelled as a Lennard-Jones site-site potential between six united carbon and hyd rogen atoms on the benzene with four interaction centres on the solven t particle. The results of the simulations are used to calculate the s econd-rank orientational order, the translational diffusion coefficien ts and second-rank rotational correlation functions of the benzene mol ecule in the isotropic, nematic and smectic B phases. The second-rank, orientational order parameters of the benzene P2bBAR and the solvent particles P2GBBAR are similar in magnitude, and show the same increase with decreasing temperature in the nematic phase as benzene dissolved in real nematic solvents. On entering the smectic B phase, P2GBBAR in creases, but P2bBAR decreases, which has also been observed experiment ally for some small solutes in smectic solvents. The calculated diffus ion coefficients parallel (D(parallel-to)) and perpendicular (D(perpen dicular-to)) to the sample director are also found to have similar mag nitudes to those found experimentally. Thus, D(parallel-to) > D(perpen dicular-to) in the nematic phase, whereas in the smectic B the reverse order holds with D(parallel-to), being essentially zero, that is, the benzene is confined to one smectic layer for the duration of the simu lation. The rotational correlation functions have the correct initial values, and all decay to their correct infinite time values within the course of the simulation. They are not single exponential decays, whi ch conflicts with the simple models often used to describe such functi ons, but is in accord with more realistic theories, such as small step rotational diffusion. The confinement of the benzene within a smectic layer does not have a large effect on the rotational correlation func tions.