Blends of Semiflexible Polymers: Interplay of Nematic Order and Phase Separation

Mixtures of semiflexible polymers with a mismatch in either their persistence lengths or their contour lengths are studied by Density Functional Theory and Molecular Dynamics simulation. Considering lyotropic solutions under good solvent conditions, the mole fraction and pressure is systematically varied for several cases of bending stiffness kappa (the normalized persistence length) and chain length N. For binary mixtures with different chain length (i.e., N-A=16, N-B=32 or 64) but the same stiffness, isotropic-nematic phase coexistence is studied. For mixtures with the same chain length (N=32) and large stiffness disparity (kappa(B)/kappa(A)=4.9 to 8), both isotropic-nematic and nematic-nematic unmixing occur. It is found that the phase diagrams may exhibit a triple point or a nematic-nematic critical point, and that coexisting phases differ appreciably in their monomer densities. The properties of the two types of chains (nematic order parameters, chain radii, etc.) in the various phases are studied in detail, and predictions on the (anisotropic) critical behavior near the critical point of nematic-nematic unmixing are made.

Automated summary

This study utilizes Density Functional Theory and Molecular Dynamics simulation to investigate mixtures of semiflexible polymers with mismatched persistence or contour lengths. By systematically varying mole fraction and pressure, the effects of bending stiffness and chain length on lyotropic solutions under good solvent conditions are explored. The phase behavior of binary mixtures with differing chain lengths or stiffness levels is analyzed, with observations of isotropic-nematic phase coexistence and unmixing in both isotropic-nematic and nematic-nematic systems. Additionally, the study delves into the detailed properties of the different chains in various phases and predicts the critical behavior near the nematic-nematic unmixing critical point.