Levitation: from drops to plastic cards

Par D. SOTO, Laboratoire Physique et Mécanique des Milieux Hétérogènes – ESPCI, France

le mardi 30 Septembre à 14h, Salle des séminaires 3e étage bâtiment A4

Manipulating drops is a major issue in microfluidics applications such as lab-on-a-chip. They are usually
conveyed in microfluidic channels and the surrounding media is commonly a liquid. However, it has lately
been shown 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. The
second one takes advantage of the viscous entrainment of the escaping air. By rectifying this flow with
microscopic textures and introducing asymmetry drops self-propel.
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. Finally, we extend this self-motion ability to rigid
objects such as glass lamellae. As we cannot exploit the Leidenfrost effect anymore, we blow air through a
porous substrate in order to nourish an insulating air-cushion.
Time-lapse of a drop spinning over two herringbone textures (in the middle) connected through two hemispherical
sections (on both sides). The white arrow is positioned at the drop starting position and shows the motion direction. The
movement lasts until there is no more liquid to evaporate.