Chemical reaction-driven tip-streaming phenomena in a pendant drop

We describe a chemical oscillatory phenomenon which occurs as follows: a pendant drop of water is immersed in a viscous oil, both phases containing reagents which react to produce a surfactant at the interface. As the drop falls away from the tip of a small needle, the remaining interface spontaneously elongates into a sharp cone and ejects small droplets from the pointed tip. The tip then either contracts and re-elongates periodically, or remains steadily elongated. Small droplets continue to be ejected in either case, and the phenomenon persists over a period of tens of minutes. Quantitative measurements connect these chemically driven phenomena with studies in four-roll mills. A mechanism is proposed by which these phenomena are sustained by Marangoni stresses. (C) 2004 American Institute of Physics.