Solvent effect on phase transition of lyotropic rigid-chain liquid crystal polymer studied by dissipative particle dynamics.

Effect of solvent quality on phase transition of lyotropic rigid-chain liquid crystal polymer is studied by dissipative particle dynamics simulation. A rod composed of fused DPD particles is used to represent the solvated rigid polymer. The effect of solvent quality is investigated by adjusting the repulsion parameter between the rods and solvent particles. The simulation shows that the solvent quality has significant influences on the phase transition behavior of the system and the influences are also closely related with the concentrations before the solvent becomes extremely poor. The influences of the solvent quality are attributed to the interplay between the immiscibility-induced phase separation and nematic-isotropic phase transition, which can be described by the binodal lines and nematic-isotropic transition lines in the phase diagrams. If a system is located in the one phase region, it will undergo a typical nematic to isotropic phase transition as the temperature increases. If a system is located in the biphasic region, there are two different types of nematic-isotropic phase transitions depending on whether the transition temperature from the biphasic region to isotropic phase region is lower or higher than the nematic-isotropic transition temperature of the concentrated phase. The first type corresponds to the transition from the biphasic region to the isotropic one phase region and the second type is attributed to the nematic-isotropic phase transition that occurs in the concentrated phase.