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Rupture d'interfaces en présence d'agents de surface

Abstract : Droplet detachment is ubiquitous in everyday life. It results from the rupture of an interface separating two fluids. This rupture has been widely studied. It is now well established that it relies on a competition between capillary, inertial and viscous phenomena. In this manuscript, we report on the influence on the breakup dynamics of the presence of surface agents at the interface. When SDS is used as a surface agent, thinning can proceed in two ways. In the first mode, the dynamics of thinning are characterized by two time-linear regimes. The second mode is made of three time-linear regimes. In both cases, thinning starts with a first regime, followed by a steeper second regime. When a third regime exists, its slope is smaller. Slope variation bears witness to a dynamical behaviour of the surfactants at the interface. The value for the interfacial tension gamma calculated from the slope of the first linear regime is in agreement with the equilibrium interfacial tension of the system, gamma_eq. The higher thinning speed during the second regime is linked to a partial depletion in surfactant of the maximal thinning zone. The slowdown in the tihrd regime is related to a displacement of the thinning zone in a region of higher surfactant concentration, where gamma is lower. The thinning dynamics is very different when polymers are added to the surfactant solution. If [SDS] is higher than 0.15 times the critical micellar concentration (CMC), a behaviour similar to the pure-surfactant case is observed. Below 0.15 CMC, an exponential slowdown is observed in the last instants, as well as a "'beads-on-a-string"' phenomenon. These observations are analogous to what is seen when a solution of polymers is led to breakup. In our case, polymers are not in the bulk ; they are at the interface of the two fluids ! Analysis of the profiles of the neck in both cases showed that profiles are self-similar. Qualitatively, they share features with profiles observed in the case of breakup of interfaces between simple fluids. Quantitatively, slopes and angles are different.
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Contributor : Matthieu Roché <>
Submitted on : Thursday, July 23, 2009 - 10:32:55 PM
Last modification on : Friday, February 15, 2019 - 8:54:02 PM
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Matthieu Roché. Rupture d'interfaces en présence d'agents de surface. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Sciences et Technologies - Bordeaux I, 2008. Français. ⟨tel-00407180⟩

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