Diffusing probe measurements in Newtonian and elastic solutions

The diffusion coefficients of polystyrene latex spheres and hematite partic les in both Newtonian and elastic liquids have been measured using dynamic light scattering. The diffusion coefficients of the latex particles measure d in glycerol/water (Newtonian) solutions obey Stokes-Einstein behaviour ov er 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 D-fast and D-slow. The appar ent fast diffusion coefficients measured in the elastic solutions show an i ncrease to a maximum, above that measured in the solvent water, with increa sing polyelectrolyte concentration. At higher polyelectrolyte concentration s the observed D-fast values decrease below the value obtained in the solve nt water. D-fast increases with the scattering vector squared (q(2)) while D-slow is independent of q(2). (C) 2001 Elsevier Science B.V. All rights re served.