Polyion Selfdiffusion in Salt‐Free Solutions of Sodium Poly(Styrene Sulfonate)

Abstract

The selfdiffusion of polyions in semidilute aqueous salt-free solutions of the linear polyelectrolyte Sodium Poly(StyreneSulf0nate) has been studied by use of Pulsed Field Gradient NMR as a function of concentration and degree of polymerization. The diffusion of the polyions was found to be only moderately dependent on polymer concentration over a large concentration range. A possible transition in diffusional behaviour, apparently independent of molecular weight, has been found to occur at a polymer concentration of about 0.05 monomolal. The molecular weight dependence of the diffusion exhibited almost Rouse-like behaviour over the concentration range under consideration for degrees of polymerization between 87 ( M , = 16ooo) and 1066 ( M , = 195000) which indicates that entanglements are probably only of minor importance. Both the concentration and molecular weight dependencies are in contrast to the behaviour of neutral polymers in the semidilute regime.Recent efforts to obtain cation hydration information from tracer diffusion measurements for a number of 2: 1 and 3: 1 electrolyte systems are described. Hydration within such systems is modelled by considering the water to be present in four different environments: coordinated to the cation, coordinated to the anion, within a loosely bound secondary hydration layer around the cation and in the bulk water environment. In order to estimate the concentration dependence of water diffusion within the bulk environment, a modified Stokes-Einstein equation, employing the viscosity ratio to a fractional power, was used.

Chain self-diffusion in aqueous salt-free solutions of sodium poly(styrenesulfonate)

“…It is noted that, as a consequence of improved data handling, diffusion coefficients in the very low concentration regime differ somewhat from preliminary results already published. 19 For larger / ratios the echo attenuation curves are not properly represented by a monoexponential decay. This can be seen in Figure lb for the case of fractions of PSS354.…”

“…Preliminary results of the present work have already been published. 19 In the second section, the experimental setup, data handling, and sample preparation are described. In the third section, results are presented for the chain selfdiffusion coefficient of sodium poly(styrenesulfonate) in water without added salt as a function of concentration for six molecular weights.…”