Percolation transitions in a binary mixture of active Brownian particles with different softness.

Homogeneous active Brownian particle (ABP) systems with purely repulsive interactions are considered to exhibit a simple phase behavior, but various physical attributes of active entities can lead to variation in the collective dynamics. Recent studies have shown that even homogeneous ABPs exhibit complex behavior due to an interplay between particle softness and motility. However, the heterogeneity in the composition of ABPs has not been explored yet.

Percolation transition in phase-separating active fluid.

The motility-induced phase separation exhibited by active particles with repulsive interactions is well known. We show that the interaction softness of active particles destabilizes the highly ordered dense phase, leading to the formation of a porous cluster which spans the system. This soft limit can also be achieved if the particle motility is increased beyond a critical value, at which the system clearly exhibits all the characteristics of a standard percolation transition.

Influence of interaction softness on phase separation of active particles.

Using a minimal model of active Brownian particles, we study the effect of a crucial parameter, namely the softness of the interparticle repulsion, on motility-induced phase separation. We show that an increase in particle softness reduces the ability of the system to phase separate and the system exhibits a delayed transition. After phase separation, the system state properties can be explained by a single relevant length scale, the effective interparticle distance.