Phase separations induced by partial stiffening of semiflexible polymers

A simple model is introduced to describe phase separations and nematic ordering in solutions and melts of semiflexible polymer chains, taking into account the partial orientational ordering of flexible bonds on the chain. We obtain the free energy by combining the Flory-Huggins theory for isotropic solutions and the Maier-Saupe model for describing the coupling between the nematic ordering and straightened bonds. Our theory predicts that the partial stiffening of the flexible bonds can be a major cause of miscibility gaps showing a bent chimney shape and triple points. We also discuss the extension of chains in a nematic phase.