Antibubble – An antibubble is a spherical shell of air suspended in a liquid and covering a liquid globule. On the picture below, spherical antibubbles are seen below the liquid surface. Before our first published work in 2003 , antibubbles were mainly a curiosity. The GRASP performed systematic experiments [1,2,3] and proposed physical interpretations about the formation and the stability of these fluidic objects. Other teams started independent studies [4,5]. A possible application of such fluid object is the delicate mixing of two miscible fluids. Another application can be found in the measurement of interfacial viscosity.
Playing with antibubbles at home - Do it yourself ! The recipe is quite simple :
1- Prepare 1/2 gallon of a water/soap solution with your favorite dishwashing detergent.
2- Fill a vessel with the mixture.
3- Clean the surface by sweeping a rigid body along the surface. Small bubbles and foam trapped at the air-liquid surface should be avoided.
4- Pour very gently the mixture at the surface. Antibubbles are formed !
Antibubble formation - The formation of an antibubble is directly linked to the liquid jet impacting the air-liquid interface (see top picture). The air film is created at the impact and the Rayleigh-Plateau instability produces antibubbles. The typical diameter of antibubbles is 1-2 cm. Thick edges are related to a total reflection of light in water. In fact, our measurements proved that the thickness of the air film is only a few microns .
Colouring antibubbles - By mixing some ink with the solution, antibubbles can be colored. This simple experiment proves that the air film separates both internal and external liquids. This suggests that liquids of different nature could be separated.
Heavy antibubbles - By adding some salt in the solution, heavy antibubbles could be created. Heavy antibubbles are more denser than the surrounding water. Such antibubbles sink and burst at the bottom of the container. When free falling, an antibubble reaches sometimes a critical pressure (critical depth) and bursts. Beautiful vortices are created (see pictures below). The occurence of a critical pressure at which all antibubbles become unstable is actually not understood. By adding glycerol in the container, a viscous layer of glycerol is formed at the bottom of the container. This viscous layer stops the free falling of heavy antibubbles.
Stability - Antibubbles are unstable objects. Indeed, air is drained from the bottom towards the top of the antibubble due to gravity. When the thickness of the air film reaches a critical length, the film breaks. The theory of air drainage in the air film  predicts an antibubble lifetime around 100 seconds. This remarkable stability still raises fundamental questions about such objects, because the antibubble lifetime is also related to surfactant molecules . The surprising relation between the lifetime and the surfactant nature found its origin in the fine analysis of air flow in the air shell. In particular, a model has been established with B. Scheid (TiPS, ULB) to take into account a coupling between the air flow and the interface. Some direct measurements by E. Rio (LPS, Orsay) seems to confirm the prediction of the model.
 S.Dorbolo, H.Caps, N.Vandewalle, Fluid instabilities in the birth and death of antibubbles, New J. Phys. 5 , 161 (2003) – PDF
 S.Dorbolo, E.Reyssat, N.Vandewalle, D.Quéré, Aging of an antibubble, Europhys. Lett. 69, 966-970 (2005) – PDF
 K.P.Galvin, S.J.Pratten, G.M.Evans, S.Biggs, Spontaneous formation of an “antidrop”, Langmuir 22, 522-523 (2006)
 P.G.Kim, J.Vogel, Antibubbles: Factors that affect their stability, Coll. Surf. A 289, 237-244 (2006)
 P.G.Kim, H.A.Stone, Dynamics of the formation of antibubbles, EPL 83, 54001 (2008)
 S.Dorbolo, D.Terwagne, R.Delhalle, J.Dujardin, N.Huet, N.Vandewalle, N.Denkov, Antibubble lifetime: Influence of the bulk viscosity and of the surface modulus of the mixture, Coll. Surf. A 365, 43-45 (2010) – PDF