Entropic Unmixing in Nematic Blends of Semiflexible Polymers*

Semiflexible polymers are ubiquitous in biological systems, e.g., in the form of double-stranded DNA or as building blocks of the cytoskeleton, and they also play an important role for various materials due to their ability to form liquid-crystalline order. We found that binary mixtures of semiflexible polymers with the same chain length but different persistence lengths separate into two coexisting different nematic phases when the osmotic pressure of the lyotropic solution is varied. Molecular Dynamics simulations and Density Functional Theory predict phase diagrams either with a triple point, where the isotropic phase coexists with two nematic phases, or a critical point of unmixing within the nematic mixture. The difference in locally preferred bond angles between the constituents drives this unmixing without any attractive interactions between monomers.