We examine the vitrification and melting of asymmetric star polymer mixtures by combining rheological measurements with mode coupling theory. We identify two types of glassy states, a single glass, in which the small component is fluid in the glassy matrix of the big one, and a double glass, in which both components are vitrified. Addition of small-star polymers leads to melting of both glasses, and the melting curve has a nonmonotonic dependence on the star-star size ratio. The phenomenon opens new ways for externally steering the rheological behavior of soft matter systems.

We explore the concentration dependence of the zero shear viscosity of well-defined dendritically branched polystyrene solutions in relation to their internal structure. Whereas in the past the change of total molecular weight was achieved via change of the number of generations (G) for fixed backbone segment length (average number of units between branches, P), these unique materials with constant number of generations allow monitoring the molecular weight through variation of P. We find that increasing P yields polymer-like behavior, whereas for lower backbone molecular weights a predominantly colloidal particle-like behavior is observed. Our results further indicate that the static properties (the branching ratio, i.e., the ratio of dendritically branched-to-linear polymer radius of gyration, g ) 〈R g 2 〉/〈Rg 2 〉linear and scattering intensity) are also sensitive, but to a lesser degree, to the crossover from colloidal to polymeric behavior, especially for the largest molecular weights.