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Levitation : from drops to plastic cards

D. Soto, PMMH, Paris

par Bodiguel Hugues - publié le , mis à jour le

Le 6 février 2014, à 14h

Manipulating drops is a major issue in microfluidics applications such as lab-on-a-chip [1]. They are usually
conveyed in microfluidic channels and the surrounding media is commonly a liquid. However, it has lately
been shown [2],[3] that there is an alternate technique for manipulating droplets based on the conjunction of
two physical phenomena. The first one relies on the levitation of the drop over a cushion of its own vapour :
the Leidenfrost effect. This insulating layer allows us to have frictionless objects, hence very mobiles [4].
The second one takes advantage of the viscous entrainment of the escaping air. As the drop is sitting on top
of the vapour layer, it squeezes it thus making a lubrication flow. By rectifying this flow with microscopic
textures and introducing asymmetry drops self-propel [5].
Here we propose to use a new texture (see Fig. 1) where we completely control the rectification of the flow,
and thus can model the role of all the physical parameters. We subsequently show new macroscopic devices
to move (see Fig. 2) or trap (see Fig. 3) drops. Finally, we extend this self-motion ability to rigid objects
such as plastic cards or PDMS flying carpets. As we cannot exploit the Leidenfrost effect anymore, we use a
porous media through which we compressed air is injected to generate an air cushion. This new set-up allows
us to explore new parameters such as the weight or the geometry of the propelled object.