Isotropic-nematic phase transition: Influence of intramolecular flexibility using a fused hard sphere model

The role of flexibility on the liquid crystal isotropic-nematic phase transition has been studied by means of Monte Carlo simulation. We present equations of state for the isotropic-nematic branches and, in the isotropic phase, numerically calculated values for the virial coefficients B-2, B-3, and B-4. We have studied two models: 11 hard sphere monomers fused in a linear configuration with a reduced bond length of 0.6 and a 15-monomer version of this model in which monomers at one end of the chain become flexible. We have observed spontaneous nematic liquid crystal formation for both of the fully rigid models, and also for models with up to six flexible monomers in the tail. We conclude that molecular flexibility has a strongly destabilizing effect on the nematic phase. This is probably due to the decrease in shape anisotropy that flexible tails allow.