Concentration fluctuation of stiff polymers. II. Dynamical structure factor of rod‐like polymers in the isotropic phase

The dynamical structure factor of the solution of rod‐like polymers is calculated by using a newly proposed kinetic equation. The initial decay rate of the structure factor is obtained as a power series of the scattering vector k. It is found that (i) the coefficient of k2, which gives the cooperative diffusion constant, increases with concentration due to the excluded volume of rod and (ii) the coefficient of k4 changes sign from positive to negative. These results agree qualitatively with experiments.