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... 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. Show less
This thesis concerns the symmetry, phase, and order parameter of the superfluid helium-3 in restricted geometries in combination with a magnetic field. Two cylindrical containers are constructed... Show moreThis thesis concerns the symmetry, phase, and order parameter of the superfluid helium-3 in restricted geometries in combination with a magnetic field. Two cylindrical containers are constructed for which the axis is aligned with the magnetic field. The first cell has a diameter (540 nm) of only a few times the size of the Cooper pairs, designed to find a new superfluid phase, namely the polar has. The second container has a diameter of 1 mm, which is the ideal size to create a potential (in the B-phase) for spin waves. To probe any superfluid phase, or spin waves, we use Nuclear Magnetic Resonance (NMR) Techniques. As the superfluids have an anisotropic susceptibility, it is an excellent tool to distinguish the different phases. However, as our samples are relatively small in volume, and the experiments needs to be performed in low magnetic field to prevent additional symmetry breaking, a very sensitive read-out magnetic resonance detection system needs to be developed, which is accomplish by creating an LC-circuit which maintains an ultra-high quality factor as it is combined with a weakly coupled transformer. Show less
