STRUCTURE FACTOR OF A SOLUTION OF CHARGED RODLIKE MACROMOLECULES IN THE ISOTROPIC-PHASE

A theory of the static and dynamical structure factor of a solution of charged rodlike polymers for the isotropic and VH-depolarized scattering was developed as an extension of our previous theory for uncharged rods. The potential of mean force was approximated with a sum of hard-rod and screened Coulomb interaction potentials. In the limit of zero polymer charge or zero Debye length, the theory reduces to the previous one for uncharged rods. The following are the major conclusions: (i) The isotropic dynamical structure factor, g(k,t), and VH-depolarized one, gVH(k,t), were given as functions of the scattering vector k, delay time t, rod length L and diameter b, polymer number concentration nu, the Debye length k-1, and polymer charge density sigma. The static structure factors g(k) and gVH(k) were also given in an approximate but analytical form. It is very easy and straightforward to evaluate the structure factors for arbitrary values of the parameters. (ii) The structure factor of a suspension of charged rods can be approximated with that of equivalent uncharged rods having an effective diameter b(eff). The approximation holds very well within a few percent of relative error, if a smaller value of the effective diameter b(eff) is used for the depolarized scattering than the one used for the isotropic scattering. (iii) The present theory is applicable to suspensions of rods, the effective axial ratio L/b(eff) of which is much larger than unity.