MONTE-CARLO AND MEAN FIELD STUDIES OF A POLYELECTROLYTE IN SALT SOLUTION

A single flexible polyelectrolyte chain in salt solution is studied by means of Monte Carlo simulations and within a mean field theory. The effect of salt has been treated both explicitly and in an approximate way using the screened Coulomb potential. The general conclusion is that the latter approximation is an excellent one for low and moderate salt concentrations of 1:1 electrolyte. The introduction of divalent ions requires a more stringent treatment in the theory including both nonlinear effects and possibly also ion-ion correlations. The mean field theory, incorporating nearest-neighbour interactions within the chain, is qualitatively correct, although it fails in the quantitative comparisons. Further extensions of the mean field theory, incorporating more explicit interactions within the polyelectrolyte chain, are discussed and it is concluded that these extensions are not likely to give a general improvement.