Collective dynamics of self-propelled nanomotors in chemically oscillating media

Abstract

The collective behavior of synthetic micro- and nano-scale motors powered by catalytic reactions has been an active research area for understanding the fundamental principles in active matter as well as their prominent applications. In many situations, small motors should operate in out-of-equilibrium complex chemically reacting media. By making use of particle-based simulations, we study the collective dynamics of chemically powered sphere-dimer motors in a chemically oscillating medium which can supply fuels to the motors and remove the products they produce. In collections of such motors, the interactions among individual motors that arise from concentration gradients and hydrodynamic coupling, are greatly influenced by the properties of the oscillation. It is shown how oscillations of the concentrations in chemical species in the environment give rise to a periodic dispersion-aggregation transition of motor clusters. The susceptibility of the transition to the oscillation is found to be changed by the manner of fuel supplies, from the time-delay response in a harmonic oscillating medium to the synchronous response in a bistable medium. The dynamical process of clusters formation, which exhibits different regimes involving propulsive and diffusive behaviors, as well as the structure of transiently formed clusters, is analyzed. The dependence of dispersion-aggregation transition on the dimer density and the frequency of periodic oscillation is presented in a phase diagram. The results presented here will contribute to the applications when an ensemble of dimers performs their tasks in complex chemical media.