Speaker
Description
Microorganisms and microscale entities swimming in fluids at low Reynolds number (Re) need to devise innovative ways of propulsion to avoid reciprocal motion [1]. A way to break the time-reversible nature of fluid flow at low Re is to use the proximity of a boundary surface. In this work, we design an innovative S-shape micro propeller that rises and levitates from a close plane due to hydrodynamic interactions with the surface. Using soft-lithography and external magnetic driving, we demonstrate the field-tunable levitation of these S-shape filaments. These propellers are made of superparamagnetic silica-coated nanoparticles in a reticulated polymer matrix assembled following a previously established microfabrication technique [2]. The filaments are dispersed in water mixed with glycerol to adjust the medium viscosity. The propellers rotate synchronously with the external field, rising and hovering at a fixed distance from the surface. We then analyze how the equilibrium height of levitation depends only on the rotating frequency of the object for a fixed viscosity of the fluid, and for a fixed size and shape of the propeller. Thus, we introduce a generic, shape-induced hydrodynamic levitation technique which can be extended to other driven or active self-propelling particles for potential applications in micro-robotics and drug-delivery in microfluidic systems.
References:
[1] E. M. Purcell; Life at low Reynolds number. Am. J. Phys. 45, 3–11 (1977).
[2] J. W. Tavacoli, et al., The fabrication and directed self-assembly of micron-sized superparamagnetic non-spherical particles. Soft Matter 9.38 (2013).
