Accurate measurement of hydrodynamic interactions between a particle and walls

International audienceA new experimental setup allows the measurement of hydrodynamic interactions between the walls of a vessel and a particle moving along a three-dimensional trajectory in a viscous fluid. The vertical motion of the particle is measured with an accuracy of 50 nm using laser interferometry, while its horizontal movements are controlled with an accuracy of 20 μm by displacing the vessel in the horizontal direction so as to keep the sphere in the fixed vertical laser beam. Three axisymmetric closed containers are used as examples: two vertical cylinders (with flat and convex lens-shaped lower walls) and a cone. Various effects of combined creeping flow hydrodynamic interactions between the particle and walls are observed