Demixing in binary mixtures with differential diffusivity at high density

TL;DR

This study investigates whether differential diffusivity can cause phase separation in dense particle mixtures, revealing demixing at high densities up to 1.0 and re-entrant behavior at even higher densities, with implications for biological tissues.

Contribution

It extends understanding of demixing driven by differential diffusivity to higher densities, including biological relevance, and compares particle models with tissue models.

Findings

Demixing occurs at packing fractions between 0.7 and 1.0.

At densities above 1.0, the system remains mixed, showing re-entrant behavior.

Confluent tissue models do not exhibit phase separation.

Abstract

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.