Thermodynamics of a polyion in a symmetric electrolyte: applicability of the Poisson-Boltzmann equation

Thermodynamics of a polyion in a symmetric electrolyte is considered using the virial expansion to the Ornstein-Zernike equation. While the Poisson-Boltzmannequation can be used to calculate the polyion electrostatic energy within a wide parameter range, it may not describe accurately the polyion-ion correlations, in particular, possible attraction between the polyion and coions in the case of a low polyion charge and high electrolyte concentration. The linear theory stemming from the virial expansion describes the electric potential around a polyion with an additional exponent besides the classical Debye-Hückel term.