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Abstract

Ferrofluids kept in place by permanent magnet quadrupoles can act as liquid walls to surround a second non-magnetic liquid inside, resulting in a liquid fluidic channel with diameter ranging from mm down to less than 10 µm. Micro particle tracking velocimetry (µPTV) experiments and modeling show that near ideal plug flow is possible in such liquid-in-liquid channels due to the reduced friction at the walls. The measured fluid velocity profiles agree with the predictions of a hydrodynamic model of cylindrical symmetry with a minimal set of hypotheses. By introducing symmetry-breaking elements in the system, we show how unique velocity and flow properties can be obtained. Our liquid-in-liquid confinement opens new possibilities for < 10 µm-sized microfluidics with low pressures and low shear, with flow characteristics not attainable in comparable solid-wall devices.