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

Abstract

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 ϕ_c is governed by the backbone stiffness N_p. 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 N_p, we observe the propagation of surface-induced nematic order above a critical stiffness N^c_p for a given ϕ. Using the simulation results N^c_p(ϕ), we construct the IN phase boundry in the ϕ–N_p plane, from which the scaling relation between ϕ_c and N_p is obtained. For semiflexible chains with N_p ≤ 5.78, our results suggest ϕ_c ∼ N_p⁻¹, consistent with prediction by Khokhlov and Semenov. For chains with N_p ≥ 5.78, we observe a new scaling regime in which ϕ_c ∼ N_p^−2/3.