Demixing in binary mixtures with differential diffusivity at high density

Spontaneous phase separation, or demixing, is important in biological phenomena such as cell sorting. In particle-based models, an open question is whether differences in diffusivity can drive such demixing. While differential-diffusivity-induced phase separation occurs in mixtures with a packing fraction up to $0.7$ [Weber et al. Phys Rev Lett 2016], here we investigate whether demixing persists at even higher densities relevant for cells. For particle packing fractions between $0.7$ and $1.0$ the system demixes, but at packing fractions above unity the system remains mixed, exposing re-entrant behavior in the phase diagram. We also find that a confluent Voronoi model for tissues does not phase separate, consistent with the highest-density particle-based simulations.