Dynamics of active run and tumble and passive particles in binary mixture

Abstract

We study a binary mixture of disk-shaped active run and tumble particles (RTPs) and passive particles on a two-dimensional substrate. Both types of particles are athermal. The particles interact through the soft repulsive potential. The activity of RTPs is controlled by tuning their tumbling rate. The system is studied for various sizes of passive particles keeping size of RTPs fixed. Hence the variables are, size ratio (S) of passive particles and RTPs, and the activity of RTPs, v. The characteristic dynamics of both RTPs and passive particles show a crossover from early-time superdiffusive to later-time diffusive. Furthermore, we observed that passive particles dynamics changes from diffusive to subdiffusive with respect to their size. Moreover, late time effective diffusivity Deff of passive particles decreases with increasing their size as in the corresponding equilibrium Stokes systems. We calculated the effective temperatures, using Deff, Ta,eff(Δ) and also using speed distribution Ta,eff(v) and compared them. The both Ta,eff(Δ) and Ta,eff(v) increases linearly with activity and are in agreement with each other. Hence we can say that an effective equilibrium can be established in such a binary mixture. Our study can be useful to study the various biological systems like; dynamics of passive organelles in cytoplasm, colloids etc. © The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature 2024.