Diffusing probe measurements in Newtonian and elastic solutions

The diffusion coefficients of polystyrene latex spheres and hematite particles in both Newtonian and elastic liquids have been measured using dynamic light scattering. The diffusion coefficients of the latex particles measured in glycerol/water (Newtonian) solutions obey Stokes-Einstein behaviour over a range of solvent viscosities and temperatures. Two apparent diffusion coefficients for the particles are measured in visco-elastic polyacrylamide and polyacrylate solutions and are designated Dfast and Dslow. The apparent fast diffusion coefficients measured in the elastic solutions show an increase to a maximum, above that measured in the solvent water, with increasing polyelectrolyte concentration. At higher polyelectrolyte concentrations the observed Dfast values decrease below the value obtained in the solvent water. Dfast increases with the scattering vector squared (q2) while Dslow, is independent of q2.