Multiple glass transitions in star polymer mixtures: Insights from theory and simulations

TL;DR

This study combines theory and simulations to explore multiple glass transition states in binary star polymer mixtures, revealing complex behaviors like double glasses and reentrant vitrification depending on size asymmetry and concentration.

Contribution

It introduces a comprehensive analysis of glass transitions in star polymer mixtures, identifying new double glass states and validating theoretical predictions with simulations.

Findings

Identification of three distinct glassy states: single, double, and a novel double glass.

Discovery of reentrant glass formation in certain parameter regimes.

Strong agreement between mode coupling theory predictions and simulation results.

Abstract

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.