  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.
