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Pulling and Pushing a Cargo With a Catalytically Active Carrier

Catalytically active particles suspended in a liquid can move due to self-phoresis by generating solute gradients via chemical reactions of the solvent occurring at parts of their surface. Such particles can be used as carriers at the micro-scale. As a simple model for a carrier-cargo system we consider a catalytically active particle connected by a thin rigid rod to a catalytically inert cargo particle. We show that the velocity of the composite strongly depends on the relative orientation of the carrier-cargo link. Accordingly, there is an optimal configuration for the linkage. The subtlety of such carriers is underscored by the observation that a spherical particle completely covered by catalyst, which is motionless when isolated, acts as a carrier once attached to a cargo.