Advances in Colloid and Interface Science 270 (2019) 73–86 Contents lists available at ScienceDirect Advances in Colloid and Interface Science journal homepage: www.elsevier.com/locate/cis Historical perspective Controlling the lifetime of antibubbles Youen Vitry a, Stéphane Dorbolo b, Jan Vermant c, Benoit Scheid a,⁎ a TIPS C.P.165/67, Université Libre de Bruxelles, Av. F. Roosevelt 50, 1050 Brussels, Belgium b GRASP, Physics Department, Building B5a, Sart-Tilman, University of Liège, B4000 Liège, Belgium c ETH Zürich, Dept. of materials, Vladimir-Prelog-Weg 5, CH-8093 Zürich, Switzerland article info abstract Article history: An antibubble is a liquid droplet wrapped by a thin layer of gas, inside a bulk liquid usually of the same 16 May 2019 composition. The lifetime of an antibubble is governed by the drainage of the gas between the two Available online 25 May 2019 liquid-gas interfaces populated by surfactants. Depending on the relative magnitude of surface viscosity and elastic moduli, which directly depend on or are determined by the nature of surfactants, the life- Keywords: time of an antibubble may vary a lot, from few seconds to few minutes. While such a difference can Surfactants be predicted with models that include the role of interfacial properties, they were not observed exper- Antibubbles Drainage imentally in previous studies, due to important sources of dispersion. In this review, the main sources of Surface viscosity dispersion are identified, such as (i) the initial amount of gas embedded in the antibubble, (ii) the level Surface elasticity of saturation of gas in the bulk liquid, (iii) the presence of dust particles (b0.5 μm) in the gas, and (iv) three-dimensional flow effects. By accounting for these various effects, we obtain a coherent view on the lifetime of an antibubble, as a function of its radius and the surface rheology, with excellent consis- tency between experiments and modeling. Results thus demonstrate that controlling the size and life- time of antibubbles is achievable. © 2019 Elsevier B.V. All rights reserved. Contents 1. Introduction............................................................... 74 2. Theory.................................................................. 75 2.1. Themodel............................................................. 75 2.2. Parametricanalysis......................................................... 76 2.3. Numericalresults......................................................... 76 3. Experiments............................................................... 78 3.1. Antibubblegenerator........................................................ 78 3.2. Materialsandmethods....................................................... 79 3.3. Surfactantcharacterization..................................................... 79 3.4. Liquidviscosity.......................................................... 80 4. Results................................................................. 80 4.1. Roleofsurfaceelasticity...................................................... 80 4.2. Influenceofinitialgasthickness................................................... 81 4.3. Influenceofgassaturation..................................................... 82 4.4. Influenceofdustparticles...................................................... 82 4.5. Othersurfactants.......................................................... 83 4.6. Three-dimensionaleffects...................................................... 83 5. Conclusions............................................................... 84 ⁎ Corresponding author. E-mail address: [email protected] (B. Scheid). https://doi.org/10.1016/j.cis.2019.05.007 0001-8686/© 2019 Elsevier B.V. All rights reserved. 74 Y. Vitry et al. / Advances in Colloid and Interface Science 270 (2019) 73–86 Acknowledgements..............................................................84 AppendixA. Originoftheinitialshellthicknessinanantibubble.........................................84 AppendixB. Supplementarydata:Modelderivation...............................................84 References...................................................................84 1. Introduction while still pinned at the tip of the capillary. Bai et al. [16] succeeded to produce antibubbles by shooting a liquid droplet onto a soap film, wrap- The antibubble owns its name for being the opposite of a soap bub- ping the drop with a shell of air: as the air-wrapped droplet reaches the ble. If a soap bubble is a thin spherical shell of soapy liquid surrounded liquid bath the external soap film coalesces with the surrounding liquid, by air, an antibubble is a thin spherical shell of air surrounded by liquid, forming the antibubble. Finally Beilharz et al. [17] determined the con- as illustrated in Fig. 1. Antibubbles have first been reported in a scientific ditions to form antibubbles by impacting a highly viscous droplet into article by Hughes and Hughes in 1932 [1]. Even though antibubbles are a liquid bath of low viscosity. Remarkably, they obtained antibubbles extremely easy to make for an amateur scientist, as nicely described in with pure liquids, i.e. without the use of surfactants. However, in such 1974 by Stong [2], not much evidences exist on the presence of a case, the lifetime of antibubbles they observed was of the order of antibubbles in nature. During the 80's in the context of boiling, Ida 100 ms only. and Takashima [3] and Nosoko and Mori [4] formed antibubbles, with- By choosing appropriate surface-active molecules, the lifetime of an out naming it, by dropping a denser volatile liquid onto a surface of an- antibubble has been obtained to range from seconds to minutes [18]. other hot liquid. Noticeably, it has recently been suggested that leaks The lifetime is the time needed for the air to drain in its shell by the ac- from subsea hydrocarbon production facilities contain antibubbles tion of gravity from the bottom, called South pole, to the top, called with a specificacousticsignature[5]. Nowadays, benefiting from the de- North pole, where it accumulates, forming an air pocket [19]. An velopment of microfluidics, several potential applications have arisen, antibubble dies when the thinning shell collapses near the South pole such as using antibubbles as contrast agent for enhancing ultrasonic im- due to van der Waals interactions [18]. An antibubble is therefore an aging [6,7] or loading the antibubble core with a ferrofluid to serve as a ephemeral object, despite the attempt to keep it alive for hours, e.g., vehicle for magneto-controlled drug delivery [8]. by shearing a confined antibubble in a spinning tube [2]orbyPickering Several configurations have been proposed to produce antibubbles. stabilization of the interfaces with colloidal particles [14,20]. Under- The most classical one being a jet impacting a liquid surface and standing what governs the lifetime of antibubbles with surfactants entraining a gas layer into a liquid bath, the antibubble resulting from alone remains therefore of prior importance. the destabilization of the air-wrapped jet inside the liquid bath [9,10]. Investigations during the last decade and a half have started on the Alternatively, Tufaile and Sarterelli [11] described the formation of an instabilities at birth and death of antibubbles [9] and on the statistics antibubble as a result of a complex coalescence process between two of their lifetimes [18], followed by an empirical description of factors af- rising bubbles formed from a submerged nozzle: as the second bubble fecting their stability [21], controlling their formation [10]orinfluenc- coalesces with the first one, a spike of liquid penetrates into the first ing their bouncing [22], and ended by experimental [23]and bubble, and destabilizes by inverted dripping into a droplet, forming theoretical [24] investigations on their collapse. In most of the experi- the antibubble. Postema et al. [12] produced micrometer-size anti- mental studies however, commercial detergents have been used to sta- bubbles by a similar mechanism of ultrasound-induced coalescence of bilize antibubbles, making it difficult to draw any conclusions on the microbubbles. Poortinga [13] and Silpe et al. [14] proposed a method mechanism responsible for their long lifetime, as detergent properties to prepare micro-antibubbles by a two-step approach: a core-shell and exact compositions are usually not well documented. water-in-oil-in-water emulsion is first generated via microfluidics and Consequently, it has not been fully clarified yet to what extent a sin- freeze-dried thereafter to yield, upon subsequent reconstitution, an gle surfactant molecule is suitable for generating antibubbles and which aqueous dispersion of antibubbles. Recently, Shen et al. [15] generated of its properties is responsible for maintaining long lifetimes. In an at- antibubbles at the outlet of a capillary dipped into a liquid and from tempt to answer this question, Dorbolo et al. [25] have demonstrated which a Taylor flow is exiting: the antibubble is produced as a result the crucial influence of surface (visco-elastic) modulus on the of the breakup of the liquid column formed into the preceding bubble antibubble lifetime, having used a mixture of three components [26], among which myristic acid, which confers to the interface very high sur- face viscosity of the order of 1 mPa.s.m. Subsequently, the role of surface viscosity to the antibubble lifetime has been rationalized theoretically by Scheid et al. [27] who showed the good agreement with experimen-