Modular phoretic micro-swimmers: from individual minimal swimmers to multi-component schools

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In this project we investigate modular phoretic micro-swimmers and closely related phenomena. Modular micro-swimmers self-organize spontaneously from inactive components and are capable of directed motion and cargo transport. Our modular approach allows for a flexible composition and optimization of components in order to improve overall performance. Using real space video-microscopy as main tool of investigation, experiments have so far been restricted to quasi 2D situations. We studied electro-osmotic pumping, minimal modular swimming and single component schooling to obtain and describe a rich phenomenology. These phenomena were investigated under systematic and controlled variation of experimental boundary conditions and the resulting behavior could be parameterized. This returned a solid quantitative data base for the development of qualitative models in close collaboration with several theoretical projects within this SPP. However, it also showed that further progress will afford an extension to a full 3D description of the motion of all components including the solvent. This shall be attempted in the second funding period. We will implement a three dimensional holographic tracking experiment and use it to continue and extend our investigations of swimming and schooling. This experiment will yield the full 3D solvent flows and thus facilitate a quantitative modeling of minimal swimming including advanced issues like downhill swimming. In addition, a number of interesting high flow situations will become accessible in great detail. These include multi-layered swarms and the formation of 3D convection structures in multi-component swarms. Moreover, 3D tracking of the solvent will strongly support the implementation of steering. As before, also high flow phenomena and novel swimmer types shall be comprehensively documented and systematically characterized. Based on these data the close collaboration with theory can be continued and extended to approach the overall goal of a refined quantitative understanding of modular phoretic micro-swimming and related phenomena.