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.