Using surface-induced ordering to probe the isotropic-to-nematic transition for semiflexible polymers.

Semiflexible polymers undergo a weakly first order isotropic-to-nematic (IN) phase transition when the volume fraction ϕ is high enough that random alignment of the backbone segments is no longer viable. For semiflexible chains, the critical volume fraction ϕc is governed by the backbone stiffness Np. To locate the IN phase transition, we perform molecular dynamics (MD) simulations of bead-spring chains confined between two impenetrable parallel surfaces. We use the impenetrable surfaces to induce nematic-isotropic interfaces for semiflexible chains in the isotropic phase. By progressively increasing the backbone stiffness Np, we observe the propagation of surface-induced nematic order above a critical stiffness N for a given ϕ. Using the simulation results N(ϕ), we construct the IN phase boundry in the ϕ-Np plane, from which the scaling relation between ϕc and Np is obtained. For semiflexible chains with Np ≤ 5.78, our results suggest ϕc ∼ Np(-1), consistent with prediction by Khokhlov and Semenov. For chains with Np ≥ 5.78, we observe a new scaling regime in which ϕc ∼ Np(-2/3).