MODIFIED POISSON-BOLTZMANN THEORY APPLIED TO LINEAR POLYELECTROLYTE SOLUTIONS

The modified Poisson-Boltzmann theory is applied to a study of the cel l model of linear polyelectrolyte solutions. The theoretical results f or polyion-simple ion correlations are compared with those obtained in parallel Monte Carlo simulations and classical Poisson-Boltzmann calc ulations for the same model. The modified Poisson-Boltzmann prediction s are found to be in complete agreement with the simulation data for m onovalent simple ions and moderate concentrations, while the Poisson-B oltzmann theory is valid at low concentrations. In solutions containin g divalent ions, where standard theories tend to give a very rough est imate of the simulated structure, the modified Poisson-Boltzmann resul ts remain very close to those obtained from the simulations. The theor y appears to provide an essentially correct account of interionic corr elations, which are neglected in mean field theory, such as the Poisso n-Boltzmann approximation, leading to poor results. The calculations f or high ionic strengths illustrate the limitations of the cell model d ue to the neglect of the correlations between double layers surroundin g neighboring polyions in solution.