Statics and Dynamics of Adhesion between Two Soap Bubbles
Résumé
An original set-up is used to study the adhesive properties of two soap bubbles put into contact. The contact angle at the line connecting the three films is extracted by image analysis of the bubbles profiles. After the initial contact, the angle rapidly reaches a static value slightly larger than the standard $120$\textdegree\ angle expected from Plateau rule. This deviation is consistent with previous studies and can be quantitatively predicted by taking into account the finite size of the Plateau border (the liquid volume trapped at the vertex) in the free energy minimization. The visco-elastic adhesion properties of the bubbles are further explored by measuring the deviation $\Delta \theta_d(t)$ of the contact angle to its static value, as the distance between the two bubbles is sinusoidally modulated. It is found to linearly increase with the imposed displacement amplitude. The in-phase and out-of-phase components of $\Delta \theta_d(t)$ are systematically probed at over a large range of frequencies. It reveals a transition from a viscous to an elastic response of the system with a crossover frequency of the order $0.2$Hz. Independent interfacial rheological measurements allow us to test several modes of deformation of the surfactant monolayers. The relevance of such adhesive dynamic properties to the rheology of foams is briefly discussed using a perturbative approach to Princen 2D model of foams.
Domaines
Matière Molle [cond-mat.soft]
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