| Summary: | 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>κ</mi></semantics></math></inline-formula> (the normalized persistence length) and chain length <i>N</i>. For binary mixtures with different chain length (i.e., <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>N</mi><mi mathvariant="normal">A</mi></msub><mo>=</mo><mn>16</mn></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>N</mi><mi mathvariant="normal">B</mi></msub><mo>=</mo><mn>32</mn></mrow></semantics></math></inline-formula> or 64) but the same stiffness, isotropic-nematic phase coexistence is studied. For mixtures with the same chain length (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>N</mi><mo>=</mo><mn>32</mn></mrow></semantics></math></inline-formula>) and large stiffness disparity (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>κ</mi><mi mathvariant="normal">B</mi></msub><mo>/</mo><msub><mi>κ</mi><mi mathvariant="normal">A</mi></msub><mo>=</mo><mn>4.9</mn></mrow></semantics></math></inline-formula> 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.
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