Dynamical Coupling between Connected Foam Films: Interface Transfer across the Menisci

Abstract

The highly confined flow of the liquid phase, trapped between the gas bubbles, is at the origin of the large effective viscosity of the liquid foams. Despite the industrial relevance of this complex fluid, the foam viscosity remains difficult to predict, because of the lack of flow characterization at the bubble scale. Using an original deformable frame, we provide the first experimental evidence of the interface transfer between a compressed film (resp. a stretched film) and its first neighbour, across their common meniscus. We measure this transfer velocity, which is a key boundary condition for local flows in foams. We also show the dramatic film thickness variation induced by this interface transfer, which may play an important role in the film thickness distribution of a 3D foam sample. arXiv:1902.07076v1 [cond-mat.soft]

Marginal regeneration in a horizontal film: Instability growth law in the nonlinear regime

“…2) and the capillary number Ca = v out /v 0 is at most of the order of 10 −4 in our experiments. The assumption of incompressible interface is valid if the Gibbs modulus E verifies E/γ Ca 2/3 ∼ 2 .10 −3 , which is the case for our foaming solution [12,15,16]. Our experiments therefore verify the theoretical assumptions (i) and (ii).…”

“…The foam film is produced on a deformable frame similar to the one used in [12], supporting three flat rectangular films and a free meniscus (see Fig. 1(a)).…”

“…After the motor has stopped, and the film has stabilized at large scale, we measure the evolution of the film thickness close to the menisci from the emission intensity of the fluorescein dissolved in the foaming solution. The calibration of the relationship between the fluorescence intensity and the thickness has been performed by measuring the film thickness along a line using a spectral camera (see [12]).…”

Rayleigh-Taylor-like instability in a foam film

“…The main goal is then to identify non-trivial features occurring at the connections between free films and menisci. Together with the fact that these clusters of films are relatively easy to build, one of their advantages is that they allow to visualize and to monitor the various flows, deformations and out-of-equilibrium film thicknesses [21]. Another advantage is that these elementary clusters can be activated on purpose: one can trigger re-organization of films, control flows in films, etc... Also -as shown in the following article -one can also easily change the setup orientation to tune the effects of gravity.…”

Micro-mechanical prediction of the effect of surfactant concentration and external friction on the visco-elasto-plastic response of an aqueous foam

“…This model extends the two-dimensional Viscous Froth model 22 , which includes the curvature of the films to simulate dry foams between parallel plates, by including the movement of surfactant molecules during foam flow 23 . As a consequence we are able to consider the tangential component of interface velocities which may be non-negligible at high deformation rate 24 . In addition to a characteristic time-scale relating to the external friction, the model has two free parameters related to the viscous and elastic properties of the interfaces.…”