Browsing by Author "Heckel, Sandra"
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- ItemBeyond Janus Geometry: Characterization of Flow Fields around Nonspherical Photocatalytic Microswimmers(Weinheim : Wiley-VCH, 2022) Heckel, Sandra; Bilsing, Clemens; Wittmann, Martin; Gemming, Thomas; Büttner, Lars; Czarske, Jürgen; Simmchen, JulianeCatalytic microswimmers that move by a phoretic mechanism in response to a self-induced chemical gradient are often obtained by the design of spherical janus microparticles, which suffer from multi-step fabrication and low yields. Approaches that circumvent laborious multi-step fabrication include the exploitation of the possibility of nonuniform catalytic activity along the surface of irregular particle shapes, local excitation or intrinsic asymmetry. Unfortunately, the effects on the generation of motion remain poorly understood. In this work, single crystalline BiVO4 microswimmers are presented that rely on a strict inherent asymmetry of charge-carrier distribution under illumination. The origin of the asymmetrical flow pattern is elucidated because of the high spatial resolution of measured flow fields around pinned BiVO4 colloids. As a result the flow from oxidative to reductive particle sides is confirmed. Distribution of oxidation and reduction reactions suggests a dominant self-electrophoretic motion mechanism with a source quadrupole as the origin of the induced flows. It is shown that the symmetry of the flow fields is broken by self-shadowing of the particles and synthetic surface defects that impact the photocatalytic activity of the microswimmers. The results demonstrate the complexity of symmetry breaking in nonspherical microswimmers and emphasize the role of self-shadowing for photocatalytic microswimmers. The findings are leading the way toward understanding of propulsion mechanisms of phoretic colloids of various shapes.
- ItemEffect of Viscosity on Microswimmers: A Comparative Study(Weinheim : Wiley, 2021) Nsamela, Audrey; Sharan, Priyanka; Garcia‐Zintzun, Aidee; Heckel, Sandra; Chattopadhyay, Purnesh; Wang, Linlin; Wittmann, Martin; Gemming, Thomas; Saenz, James; Simmchen, JulianeAlthough many biological fluids like blood and mucus exhibit high viscosities, there are still many open questions concerning the swimming behavior of microswimmers in highly viscous media, limiting research to idealized laboratory conditions instead of application-oriented scenarios. Here, we analyze the effect of viscosity on the swimming speed and motion pattern of four kinds of microswimmers of different sizes which move by contrasting propulsion mechanisms: two biological swimmers (bovine sperm cells and Bacillus subtilis bacteria) which move by different bending patterns of their flagella and two artificial swimmers with catalytic propulsion mechanisms (alginate microtubes and Janus Pt@SiO2 spherical microparticles). Experiments consider two different media (glycerol and methylcellulose) with increasing viscosity, but also the impact of surface tension, catalyst activity and diffusion coefficients are discussed and evaluated.