Festoon instability of a drop of volatile insoluble liquid on the surface of other liquid under evaporation cooling conditions

摘要

A festoon structure having the form of round hills has been observed at the periphery of a drop of o-xylene or isooctane lying on the surface of a layer of hot water. On reaching a diameter of about 1 mm, festoons are ejected toward the drop center at a velocity of 1-2 mm/s. The growth of festoons is caused by thermocapillary flows, while their ejection is related to the capillary forces, which tend to decrease the free surface. This kind of stability substantially differs from the other known thermocapillary instabilities, since the ejection of festoons prevents the drop from spreading and thus prolongs its life.