  We study the electric double layer near a charged soft surface by using a
mean-field approach including non-uniform size effect and solvent polarization.
Based on a free energy model, electrostatic potential and number densities of
water and ions are obtained numerically by solving coupled differential
equations including the Poisson's equation. We find that the solvent
polarization significantly affects electrostatic potential, ion number
densities and permittivity in an electrolyte solution near a charged soft
surface. We prove that the consideration of the solvent polarization increases
the magnitude of Donnan potential. We also demonstrate that within the fixed
charge layer the number densities of counterions and coions are slightly
smaller than when the solvent polarization is not considered. An increase in
the ionic size enhances the influence of solvent polarization on the
electrostatic properties within the fixed charged layer of charged soft
surface. In the region of high surface-charge-density, the permittivity and the
number density of water dipoles considerably decrease due to water
polarization.
