Synthetic model microswimmers near walls

Ketzetzi, S.

Synthetic microswimmers take an important place within the interdisciplinary field of active soft matter. Many efforts are being made to develop, understand and ultimately control them, because of their great potential for fundamental studies and applications. A widely employed type is that of catalytically propelled microswimmers, such as platinum-half-coated colloids which achieve self-propulsion in aqueous hydrogen peroxide environments via a catalytic reaction taking place on the platinum. Surprisingly, although these swimmers are typically found self-propelling parallel to walls, the origins for this near-wall behavior and the influence of the walls are still largely unexplored. In this thesis, we examine the behavior of catalytic microswimmers near walls. We find that the physical property of slip of the nearby wall significantly impacts their speed. We develop a new diffusion-based analysis method, and uncover that swimmers tend to fixed heights above planar walls. Using...Show moreSynthetic microswimmers take an important place within the interdisciplinary field of active soft matter. Many efforts are being made to develop, understand and ultimately control them, because of their great potential for fundamental studies and applications. A widely employed type is that of catalytically propelled microswimmers, such as platinum-half-coated colloids which achieve self-propulsion in aqueous hydrogen peroxide environments via a catalytic reaction taking place on the platinum. Surprisingly, although these swimmers are typically found self-propelling parallel to walls, the origins for this near-wall behavior and the influence of the walls are still largely unexplored. In this thesis, we examine the behavior of catalytic microswimmers near walls. We find that the physical property of slip of the nearby wall significantly impacts their speed. We develop a new diffusion-based analysis method, and uncover that swimmers tend to fixed heights above planar walls. Using obstacles of different shapes 3D-printed on the planar wall, we found cooperative swimmer behaviors along one-dimensional environments. Overall, our findings provide new insights into the still-debated propulsion mechanism of catalytic microswimmers, and may also aid in predicting and controlling swimmer motions in future applications, where synthetic swimmers will be needed to perform tasks inside complex environments.
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