Formation of liquid marbles and wetting transitions.

The formation of liquid marbles was studied in the situation where hydrophobic particles coating the marbles "come from air". Droplets of water/ethanol solutions of various concentrations were coated with three kinds of powders: polytetrafluoroethylene, polyvinylidene fluoride and polyethylene. We established that there exists a critical concentration of ethanol, and correspondingly a critical surface tension of the water/ethanol solution allowing formation of liquid marbles. A critical surface tension depends on the kind of the powder. In parallel, wetting transitions of water/ethanol solutions were studied on the layers of the same polymer powders. The onset of wetting transitions on the powders took place at the concentrations of ethanol coinciding with those enabling the formation of liquid marbles. Wetting transitions stipulate the formation of liquid marbles when a droplet is deposited on a layer of hydrophobic powder. This assumption was validated by the experiments performed with di-iodomethane and glycerol.