Solutions of highly charged polyelectrolyte chains are described by a model that introduces ion condensation as a random charge along the polymer. The degree of condensation is obtained by solving the Poisson-Boltzmann equation with cylindrical geometry. Short range electrostatic attractions between the monomers via the condensed counterions of high enough valency lead to reversible chain precipitation. The range of polymer concentration over which salt-free solutions are unstable is determined, as well as the miscibility of the chains when salt is added. Redissolution at high salt concentration is due to a screening of the short range electrostatic attractions. Precipitation of chains in mixtures of movalent and multivalent salts is also studied. We find the range of salt concentration where chains precipitate. The model explains the experimental results on the precipitation of sodium and lanthanum polystyrene sulfonate solutions in presence of multivalent salts ͓LaCl 3 and Th͑NO 3 ͒ 4 ͔.

Light-scattering studies of polyelectrolyte solutions without added salt have been made near the transition dilute/semidilute regime. Aqueous solutions of sodium poly(styrenesu1fonate) (molecular weight: 7.8 X lo5) with concentrations from lo-' to 4 X lo-* g/L show a q dependence of both the scattered intensity and the effective diffusion coefficient. The scattered intensity is characterized by a broad peak for q between A-1. This result is similar to those obtained by small-angle neutron-scattering experiments in the concentrated regime. The q value corresponding to the maximum intensity varies as C'I2 for the whole range of concentrations. The diffusion coefficient shows a clear minimum around q values where the maximum in the structure factor ( q M ) is observed. The experimental results are consistent with a short and local ordering due to the long-range Coulombic interactions of slightly flexible chains near the rod limit. and 3 X The pulse radiolysis of benzophenone in liquid 1-propanol was investigated within a large temperature range. At temperatures lower than 180 K the absorption spectrum of benzophenone anion is time dependent. The blue shift observed after the pulse is attributed to the reorientation of alcohol molecules around the aromatic anion which was formed in a presolvated state. The kinetics of this spectral shift was studied as a function of temperature. Comparison with the dielectric relaxation times in 1-propanol shows that the rate-determining step is the breaking of solvent hydrogen bonds. The possibility that part of the spectral shift is due to the formation of a hydrogen bond between the solvent and the anion is discussed.

SynopsisThe quasielastic light scattering method was used to study the ionic strength dependence of the mutual diffusion coefficient of sodium polystyrene sulfonate (NaPSS) as a function of NaCl and CaC1, concentrations. The results indicate a splitting in the relaxation times that depends on the ratio C,/ C,, where C, and C, are the polyion and added salt concentrations. A universal relationship taking into account Manning's theory of condensation and the Debye screening due to the added salt is proposed to characterize the fast-slow relaxation time transition.