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 $\delta$ and concentration $\rho_2$ 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 $\delta$ and low $\rho_2$, a double glass at high $\delta$ and low $\rho_2$, and a novel double glass at high $\rho_2$ and high $\delta$ which is characterized by a strong localization of the small particles. At low $\delta$ and high $\rho_2$ there is a competition between vitrification and phase separation. Centered in the $(\delta, \rho_2)$-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.Comment: 15 figures, to be published in Macromolecule

The Information Content Of Multiple Scattering Data: Monte Carlo And Laboratory Experiments

A new computer simulation methodology is developed which determines the structure factor, S(q), of concentrated suspensions accurately and subsequently calculates S(q) from the wavelength dependence of the transport mean free path , l*(λ), for the same systems. Therefore our method can test directly the validity of approximations involved in the analysis of multiple scattering data. The simulation results for l* agree closely with experimental data and explain the substantial overestimation of l* by the photon diffusion formula [1, 2] observed in some experiments. © Springer-Verlag 2001