Spontaneous formation of an "antidrop".

We have observed, with great surprise, the spontaneous formation of a quite unusual drop. Because of its similarity to the antibubble [(a) Hughes, W.; Hughes, A. R. Nature 1932, 129 (3245), 59. (b) Skogen, N. Am. J. Phys. 1956, 24, 239. (c) Strong, C. L. Sci. Am. 1974, 230 (4), 116.], we describe our find as an "antidrop", a thin spherical shell of an aqueous salt solution, surrounded by an inner and outer organic liquid phase. Two of these antidrops, about 8 mm in diameter, are shown in the present paper resting on a bed of smaller conventional drops. Drops of this size do not normally appear so spherical, however the antidrop is a mere shell, and hence its geometry is dominated by the interfacial tension. We found these drops to be remarkably stable, given it was possible to reversibly deform the drops and even slice through a drop with a glass rod to produce two antidrops. Ultimately, after some finite time period, the antidrops simply disintegrated into clouds of tiny droplets of the aqueous salt solution because of the drainage and concomitant rupturing of the liquid comprising their thin spherical shells.