Quantitative treatment of rotational diffusion of entangled rodlike polymer molecules in semidilute solution is extended to include anisotropy in the orientational distribution of rods. Noting that anisotropy has a similar effect to changing the polymer concentration of the size and form of a tube confining a rodlike molecule, we apply the mean-field argument to the hindered diffusion of entangled rods. The rotational diffusion constant, which depends not only on the orientation but also on the diffusion direction, is derived as a functional of the orientational distribution function. As an example of external force which causes anisotropy, we study stationary elongational flow and obtain the rotational diffusion constant self-consistently as a function of the strain rate. It is found the tube is not a round but an oblate cylinder.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry