No abstract

We introduce a dynamic scaling hypothesis which connects the self-diffusion of a chain with the viscosity of the macromolecular solution. It applies to both semidilute and concentrated solutions and leaves the detailed motion of the chains unspecified. When it is valid, one is able to measure the density v of effective dynamic units in the transient network of entangled chains. The feasibility of the hypothesis is shown for aqueous poly(ethy1ene oxide) and sodium poly(styrenesulfonate), polymers not at all conforming to the usual scaling dynamics. Surprisingly, the density v is not very sensitive to charge or the addition of salt.

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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.