The oscillation spectrum of a compound drop

Under microgravity conditions the equilibrium shape of a compound drop, consisting of two immiscible mutually wetting liquids, is given by a spherical liquid core, encapsulated by the second liquid phase. Due to energy considerations, the outer liquid is the one with the lower (vapour-liquid) surface tension. The oscillation spectrum of such a compound drop corresponds to that of two coupled oscillators, one being driven by the surface tension, while the other is due to the interfacial (liquid-liquid) tension between the two immiscible liquids. Therefore, in principle, the values of both, the surface and the interfacial tension, can be derived from the frequencies of the coupled oscillations. In this paper, an analytic expression is presented, relating the frequency spectrum to the surface and interfacial tension, respectively. In addition, the concept for technical realisation using electromagnetic levitation and copper-cobalt as a model system, is discussed. C 2005 Springer Science + Business Media, Inc.