Intrinsic viscosities of polyelectrolytes: specific salt effects and viscometric master curves

Abstract

Dilute solutions of the sodium salt of polystyrene sulfonic acid (PSS-Na) were measured viscometrically as a function of composition in aqueous solvents of different salinity, where the extra salt was either NaCl or CaCl₂. Such experiments yield {η}, the generalized intrinsic viscosities (hydrodynamic specific volume) of the polyelectrolyte for arbitrary polymer concentrations, c. In the limit of infinite dilution {η} becomes identical to the intrinsic viscosity [η]. For NaCl {η} decreases monotonously with rising c, whereas maxima are passed in the case of CaCl₂. Condensing c and the concentration of extra salt in the mixed solvent into a single variable enables the establishment of predictive master curves. The viscometrically observed changes in the spatial extension of the individual polymer coils are discussed in light of the corresponding thermodynamic information.