Theory of nematic systems of semiflexible polymers. III. Phase equilibria in solutions.

Biphasic equilibria of lyotropic solutions of semiflexible polymers are calculated using the worm-like chain model with limiting curvature. The threshold concentration at incipient phase separation varies gradually with molecular weight to reach a finite value at infinite chain length. This limiting concentration is found to depend on the axial ratio of the persistence length and on the temperature. The theory is then applied specifically to poly(n-hexyl isocyanate) (PHIC) solutions. Deriving the configurational parameters from measurements on chain dimensions in dilute solutions, theoretical calculations are found to satisfactorily match recent experimental results on the molecular weight dependence of the threshold concentration of PHIC in toluene. [ABSTRACT FROM AUTHOR]