Biaxiality of cholesteric phases in rod-like polymer solutions

A mean field theory for the biaxiality of a cholesteric phase in rod-like polymer solutions is presented. By taking into account both excluded volume and attractive interactions between rods, we calculate the biaxiality of the cholesteric phase as a function of temperature and concentration. At low concentrations of rods, the biaxiality increases with increasing temperature. At high concentrations above phi = (D/L)3.5, the biaxiality becomes the maximum as a function of temperature. We also calculate phase diagrams on the temperature-concentration plane and study phase separations between an isotropic phase and a biaxial cholesteric phase.