Controlling the dynamics of soft spheres: From polymeric to colloidal behavior

We probe the dynamic structure factor of multiarm star polymer solutions in good solvent above the overlap concentration with photon correlation spectroscopy and NMR. With the aid of a mean-field theoretical approach, which accounts for the interplay between the topologically enhanced osmotic pressure and the arm entropic stretching, we identify three mechanisms for relaxing the concentration and density fluctuations: cooperative diffusion, self-diffusion and structural relaxation. These model spherical brushes exhibit a behavior intermediate between polymers and colloids