Activity-modulated phase transition in a two-dimensional mixture of active and passive colloids.

We study a two-dimensional binary mixture of active and passive colloids as an idealized model of an hybrid aggregate of living cells and inert particles. We perform molecular dynamics simulations of this system using two different thermostats, and we systematically investigate the effect of varying these two effective temperatures on the system behavior, as characterized by its density, structure and thermoelastic properties. Our results indicate that the presence of active colloids shifts the mixture towards the liquid state and renders it more deformable. Such system softening and melting effects due to the addition of active particles are larger than expected from a linear combination of temperatures of the active and passive components. This heightened effect becomes more pronounced as the effective temperature difference between the two components becomes larger. The binary mixture remains homogeneous for moderate colloidal activity, but segregation arises for large effective temperature difference. Our results provide insights to guide future experimental hybrid aggregate studies with promising biomedical applications.