Spherical polymeric brushes viewed as soft colloidal particles: Zero-shear viscosity

We examine the concentration dependence of the zero-shear viscosity of two chemically distinct classes of spherical brushes, multiarm star polymers and giant diblock copolymer micelles. We show that the effective volume fraction based on the hydrodynamic, rather than the static, size of these objects is the appropriate scaling parameter for obtaining a generic description of the relative viscosity for systems of varying size and softness. We demonstrate that it is possible to span the whole range from polymeric behavior to that of hard colloidal spheres by tuning the sphere softness at the molecular level (arm size and functionality).