Phase separation kinetics of a symmetric binary mixture of glass-forming liquids

Abstract

Mixtures of glass-forming fluids sometimes exhibit glass-glass phase separation at low temperatures. Here, we use a molecular dynamics simulation to study one of the simplest examples of the glass-glass phase separation. We consider a mixture composed of type A and B particles, in which the A-A and B-B interactions are the identical Lennard-Jones interactions and the A-B interaction is repulsive only. To avoid crystallization, we also introduce the polydispersity in the particle sizes for each component. We study the phase separation kinetics of this model at a 50:50 concentration at various temperatures. We find that hydrodynamic coarsening takes place when the temperature is higher than the onset temperature of the glassy dynamics. At lower temperatures, diffusive coarsening is observed over a long duration, and a further slower coarsening appears within a shorter time. Below the glass transition temperature, the domain growth does not stop but becomes logarithmically slow or even slower than logarithmic. By analyzing two-time correlation functions, we show that these slow coarsening processes are accompanied by a slowing down of the microscopic dynamics, which has qualitative similarities with the aging dynamics without phase separation. Based on the results, we discuss a possible link between the slow coarsening and the aging-like microscopic slowing down in the glass-glass phase separation.