Susceptibility of liquid-crystalline solutions of semiflexible macromolecules in an external orientational field

The susceptibility of solutions of semiflexible macromolecules in an external orientational field of the dipole type is considered both for the isotropic and the liquid-crystalline phases. It is shown that the concentration dependence of the zero-field susceptibility in the anisotropic phase depends essentially on the character of the flexibility distribution along the chain contour. For a localised flexibility mechanism (freely jointed chain) the susceptibility in the anisotropic phase is practically independent of concentration, whereas for a persistent flexibility mechanism it increases exponentially with concentration. Similar differences exist in the concentration dependence of the mean-square end-to-end distance for freely jointed and persistent macromolecules in the anisotropic phase. In an Appendix it is shown that the problem under consideration is analogous to the well known quantum mechanical problem of the energetic spectrum of a particle in two identical wells separated by a high potential barrier.