A MEAN-FIELD THEORY FOR THE SWELLING OF A GAUSSIAN POLYION

The effect of electrostatic forces among the ionized units on the structure of a polyion is studied using a simplified mean-field model that represents the polymer as a swollen Gaussian coil. Screened Coulombic interactions are approximated by the pairwise additive Yukawa potential. The swelling parameter is estimated in a variational procedure analogous to Flory's theory for neutral polymers. The analytic solution to the variational problem is given. The method is shown to provide a fair description of the polyion configuration at lower ionization or in the presence of moderate concentrations of simple salt in the solution.