Self-Propulsion of Chemically Active Micro-Particles

Self-Propeller Synthetic micro-motors which can move cargo in a well controlled way through a liquid environment are of significant interest for applications such as targeted drug delivery, biosensing, and shuttle-transport of living cells. One promising approach is to use catalytically active Janus colloidal particles as model micro-motors. This type of particles harvest chemical free energy from the surrounding liquid environment and then transform it into mechanical energy. Due to an asymmetric decoration of their surface with a catalyst, which promotes a specific chemical reaction in the surrounding liquid, concentration gradients of the reaction products develop along the surface of the particle. Depending on the systems, various self-propulsion mechanisms emerge, such as bubble propulsion, self- electrophoresis, or self-diffusiophoresis, which in some systems can be activated by light.

We are investigating how self-diffusiophoresis, i.e. self-propulsion due to self-generated electrically neutral solute gradients, depends on the self-propeller's shape and the extent of the catalyst coverage, how Janus micro-motors could be used as carriers of micro-cargo or how the motion of an active particle is influenced by the presence of confining walls. In our recent work, we have shown that an active Janus particle moving near a wall reveals a very rich behavior, including novel sliding and hovering steady states. Sliding states, for example, could provide a starting point to establish a stable and predictable motion of swimmers in microdevices. Hovering particles create recirculating regions of flow, and could be used to mix fluid or to trap other particles.
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