Multiple Glass Transitions in Star Polymer Mixtures: Insights from Theory and Simulations

The glass transition in binary mixtures of star polymers is studied by mode coupling theory and extensive molecular dynamics computer simulations. In particular, we have explored vitrification in the parameter space of size asymmetry δ and concentration ρ2 of the small star polymers at fixed concentration of the large ones. Depending on the choice of parameters, three different glassy states are identified: a single glass of big polymers at low δ and low ρ2, a double glass at high δ and low ρ2, and a novel double glass at high ρ2 and high δ which is characterized by a strong localization of the small particles. At low δ and high ρ2 there is a competition between vitrification and phase separation. Centered in the (δ, ρ2)-plane, a liquid lake shows up revealing reentrant glass formation. We compare the behavior of the dynamical density correlators with the predictions of the theory and find remarkable agreement between the two.