ABSTRACT
The manipulation of droplets becomes a huge problem as soon as tiny quantities of liquid have to interact with micro-sensors or with another liquid. A broad range of applications can be found in food science, pharmacology, coating, painting and biotechnology among others. Droplets can be used in chemical engineering in order to mix tiny amounts of reactive substances. To achieve such a goal, one has to invent some processes to manipulate a droplet: motion, binary collision, fragmentation, . . . Most of efforts were made in the framework of microfluidic [1], i.e. the droplets are driven through close channels using a second liquid (non-miscible with the liquid of the droplet). That technique requires a perfect control of the surface properties: wetting, de-wetting, pinning of the contact line, . . . Accurate pumps are needed
to drive the droplet through the network of channels. Finally, the contamination should be prevented by avoiding any contact with a solid element. An alternative technique to the microfluidic channels consists in manipulating individual droplets onto a liquid bath.
