Europhys. Lett., 76 (2), pp. 236–242 (2006) DOI: 10.1209/epl/i2006-10262-x EUROPHYSICS LETTERS 15 October 2006 Bursting of a fluid film in a viscous environment ´ E. Reyssat and D. Qu´ er´ e Physique et M´ecanique des Milieux H´et´erog`enes, UMR 7636 du CNRS, ESPCI 75005 Paris, France received 16 March 2006; accepted in final form 25 August 2006 published online 22 September 2006 PACS. 47.55.N- – Interfacial flows. PACS. 68.03.Cd – Surface tension and related phenomena. PACS. 68.15.+e – Liquid thin films. Abstract. – The dynamics of break-up of soap films is usually limited by an inertial resistance. We present here experimental results on the retraction of a fluid sheet in a viscous atmosphere. The border of the film is observed to form a rim, which retracts at a constant velocity. Con- trasting with usual soap films, the bursting dynamics is limited by the friction arising from the presence of a viscous environment. A simple model is developed to explain these results. Introduction. – Owing to its large surface area, a suspended liquid film is metastable: a hole nucleated in the film is drawn by surface tension, which opens it till complete transfor- mation into droplets. The most familiar such case is the explosion of a soap bubble, whose dynamics was investigated long ago, in particular by Taylor, Culick and Mysels [1–3]. Since the event is extremely fast (a centimetric bubble explodes in typically 10ms), liquid inertia was as- sumed to be the main cause of resistance to bursting. For very viscous films, viscous dissipation can also moderate the bursting, as discussed more recently by Debregeas [4] and Brenner [5]. The outer atmosphere may also play a role in the dynamics of the explosion. A film retracting very fast induces friction on the environing fluid, leading to small corrections in the bursting kinetics. This force may even become dominant if the viscosity contrast is reversed, as emphasized by Joanny and de Gennes [6]. If a fluid film bursts in a viscous atmosphere, the explosion is much slower, because of a large dissipation in the environing fluid. This situation might be encountered in oil/water emulsions: as coalescence between adjacent drops takes place, water films retract in a viscous oil. It also concerns the bursting of so-called antibubbles, where unstable air films surround globules of water, the whole being immersed in water [7]. Similarly, as a jet quickly enters a bath of the same liquid, it gets coated by a film of air, which tends to retract [8]. This situation is also close to what is observed as a film of low viscosity dewets on a very viscous liquid: then, as shown by Martin et al. the dewetting velocity is fixed by the presence of a viscous substrate [9]. In this paper we present experiments on the bursting of fluid films (either water, or air) placed in a viscous atmosphere. A simple model is provided to explain the observed bursting speeds, and we compare our findings to Martin’s ones for mobile films dewetting on viscous substrates. We finally describe a specific instability, which is likely to occur during explosion. c  EDP Sciences Article published by EDP Sciences and available at http://www.edpsciences.org/epl or http://dx.doi.org/10.1209/epl/i2006-10262-x