Predicting nematic phases of semiflexible polymers

The nematic coupling constant α, together with the chain stiffness κ, governs chain alignment and the isotropic-to-nematic (IN) transition temperature T_IN for semiflexible polymers. We combine self-consistent field theory (SCFT) with atomistic molecular dynamics (MD) simulations of semiflexible chains under external tension in the isotropic phase to determine the nematic coupling constant α. Using α, we obtain the variational free energy of a multichain system, from which the IN transition temperature T_IN can be calculated. We apply our method to obtain α and T_IN of a commonly studied semiflexible conjugated polymer, poly(3-hexylthiophene) (P3HT). We predict T_IN to be above the crystal melting temperature T_m for P3HT and to follow T_IN(S) = 535K(1 - 1.64/S), in which S is the number of monomers.