ABSTRACT
Many natural and artificial systems consist of several diversely sized entities that act together, producing dazzling self-organized patterns. The role of bidispersity in size on the segregation dynamics of self-propelling particles placed inside an enclosure is examined in exhaustive detail, showcasing the diverse behavior exhibited by these particles. A two-dimensional discrete element method model is formulated for these active particles, and the emergence of collective motion due to the interplay of self-propulsion, collision, and drag interactions is analyzed. The active particles are designed as soft disks moving in a Stokes flow regime, resulting in a linear hydrodynamic drag. Depending on the drag force acting on the particles; different non-equilibrium steady states are observed in simulations: (i) milling motion at low and moderate drag and (ii) oscillatory motion at high values of the drag coefficient. A segregation index is calculated to study the effect of the degree of bidispersity and packing fraction on the transition between the regimes. A higher concentration of smaller particles in the domain leads to greater penetration into the layer of larger particles, hence providing greater mixing. Our findings provide specific insights regarding the interaction of active particles, their mixing, and segregation induced by differences in size.
