CONTROLLING THE DYNAMICS OF SOFT SPHERES - FROM POLYMERIC TO COLLOIDAL BEHAVIOR

We probe the dynamic structure factor of multiarm star polymer solutio ns in good solvent above the overlap concentration with photon correla tion spectroscopy and NMR. With the aid of a mean-field theoretical ap proach, which accounts for the interplay between the topologically enh anced osmotic pressure and the arm entropic stretching, we identify th ree mechanisms for relaxing the concentration and density fluctuations : cooperative diffusion, self-diffusion and structural relaxation. The se model spherical brushes exhibit a behavior intermediate between pol ymers and colloids.