Dynamics of concentrated solutions of rigid-chain polymers. Part 1.—Brownian motion of persistent macromolecules in isotropic solution

Abstract

A molecular theory for the dynamics of rigid-chain polymers in concentrated solutions, based on reptation ideas, is presented. It is shown that partial flexibility of the macromolecules plays an important role in the dynamics of the polymer solution. A diffusion equation which describes the Brownian motion of macromolecules is constructed. The relaxation of the Kerr effect is considered and the rotation–diffusion coefficient is calculated. The relaxation of the macromolecular structure factor and time correlation function of polymer density (dynamic form factor) are considered also. In particular it is shown that (i) the relaxation of the Kerr effect must be non-exponential in all cases when the length of macromolecules L is larger than the effective Kuhn segment l; (ii) the relaxation of the structure factor S(q,t) in the region q²Ll≫ 1, L≈l is described by three characteristic times; and (iii) the cooperative diffusion coefficient of macromolecules in concentrated solution is always much larger than the self-diffusion coefficient.