Polyelectrolyte solutions without added salt. Concentration effects and condensation

Abstract

Concentration effects in salt-free polyelectrolyte solutions are discussed in terms of scaling relations as proposed by Odijk. No explicit use is made however of the condensation approach and all important quantities are expressed in terms of an effective charge density parameter. It is shown that, in the concentration range most accessible to experimental investigation, the exact value of this parameter may have strong bearings on the applicability of the theory and its conclusions. The condensation approach is discussed in terms of the analytical solution of the Poisson-Boltzmann equation for salt-free polyelectrolyte solutions and its validity questioned in the same concentration range. Comparison of the Poisson-Boltzmann solution for the potential at the surface of the charged polyelectrolyte with values derived from filtration data of a weak polyacid shows qualitative agreement but suggests that the effective charge density parameter may be different from its structural value.