Collective dynamics of self-propelled sphere-dimer motors

The collective dynamics of ensembles of chemically powered sphere dimer motors is investigated. Sphere dimers are self-propelled nanomotors built from linked catalytic and noncatalytic spheres. They consume fuel in the environment and utilize the resulting self-generated concentration gradients to produce directed motion along their internuclear axes. In collections of such motors, the individual motors interact through forces that arise from concentration gradients, hydrodynamic coupling, and direct intermolecular forces. Under nonequilibrium conditions it is found that the sphere dimer motors self-assemble into transient aggregates with distinctive structural correlations and exhibit swarming where the aggregates propagate through the system. The mean square displacement of a dimer motor in the ensemble displays short-time ballistic and long-time diffusive regimes and, for ensembles containing many motors, an increasingly prominent intermediate regime. The self-diffusion coefficient of a motor in a many-motor system behaves differently from that of an isolated motor, and the decay of orientational correlations is a nonmonotonic function of the number of motors. The results presented here illustrate the phenomena to be expected in applications, such as cargo transport, where many motors may act in consort.