At length scales of micro- or nanometers, swimming becomes an almost impossible task as Brownian motion is shaking all microscopic swimmers and normal time-symmetric swimming movements cause no progress. At the microscale other mechanisms have to be found to transport objects actively. Evolution, for example, has brought up molecular motors, which are confined to tracks in cells to enable transport.
Here, we investigate new mechanisms which propel particles or which allow the trapping of molecules in solution. These mechanisms mainly involve temperature as one of the key parameters of Brownian motion. By generating temperature gradients in various geometries, we steer, trap and propel particles. Our research aims at the creation of small nanomachines and the development of artificially intelligent systems to uncover, which information flows are required to create collective behavior which is essential for life. Further a number of new phenomena of statistical mechanics are studied in these non-equilibrium systems.
Photon Nudging is an advanced control technique for artificial micro swimmers, which we have developed with the group of Prof. Haw Yang at the chemistry department at Princeton University. Due to the rotational Brownian motion of micro swimmers, their directional motion only persists for a short time. To make the motion persistent, we harness for the first time thermal fluctuations in the spirit of a Maxwell demon. Photon Nudging follows the orientation of single artificial micro swimmers in realtime to switch the propulsion of the micro swimmer on or off depending on its orientation towards a target location. By doing that a motion much like the famous run-and-tumble motion of E-coli batteries arise and the swimmer is able to steer along path and to be localized on target positions.
This technique is the foundation for all other swimmer control experiments in the group. It allows us to explore the interaction of a controlled number of particles to reveal what hydrodynamic and thermal interaction rules they obey.
Interactions of Swimmers
Information Flow and Artificial Swimmer Molecules
In living systems information flow plays an important role for self organization. A flock of birds for example adjusts to a certain density based on the interactions of individual swimmers, which are not physical but based the information a bird acquires about the rest of the flock and how it responds to this information.
Here we introduce similar information based interactions between swimmers, by constructing simple feedback rules between individual swimmers.