The fizzling foam of champagne.

Bubble, bubble: why does champagne bubble? Why does it stop bubbling? Does the vintage affect its fizz? Chemistry can answer these and other questions about the wine that is so often associated with celebrations and anniversaries.

Dynamics of yielding observed in a three-dimensional aqueous dry foam.

We study the onset of yielding in stable three-dimensional dry foams following the start up of steady shear flow. By means of a charge-coupled device camera equipped with a small depth-of-field objective, we visualize the Plateau border network in the bulk of the foam. The onset of yielding is identified with the deformation gamma(c) for which shear induced rearrangements start occurring. We show that gamma(c) is independent of shear rate gamma; in a quasistatic regime whereas at high strain rates, a rapid increase of gamma(c) with gamma; is observed, in qualitative agreement with theoretical models. Moreover, spatiotemporal image analyses are used to determine the velocity profile in the gap. We find that this profile remains linear up to strains far beyond gamma(c). Moreover, we have studied the strain history dependence of gamma(c).

Foam drainage in the presence of nanoparticle-surfactant mixtures.

The drainage of SiO(2) nanoparticle-cationic surfactant (TTAB) mixtures through calibrated aqueous foams had been studied by combining several approaches on both the macroscopic and the local scale. Macroscopic measurements reveal a strong stabilizing effect arising for nanoparticle concentrations as low as 2 wt % mainly because of a drainage kinetic slow-down dependent on the nanoparticle concentration. We show that the variation of the viscous parameters (bulk viscosity, interfacial viscosity, or both) in the classical theoretical models of foam drainage, mainly developed for aqueous surfactant solutions, does not enable fitting experimental data obtained via steady- or free-drainage strategies for [SiO(2)] > or = 2 wt %. In contrast, the quantitative analysis of the data obtained from front propagation velocities has revealed a drainage regime transition from a node-dominated regime toward a Plateau-border-dominated regime upon nanoparticle concentration increase. Observations performed at the Plateau border scale brought to light the drainage kinetic slow-down process by evidencing that the presence of insoluble aggregates induces traffic jamming and even cork formation for silica concentrations above 2 wt %. Considering these observations, a simple mechanism of aggregate growth and cork formation is proposed. Finally, we analyze the discrepancy between experiments (steady- and free-drainage methods) and theory by pointing out that the hypothesis relative to the foam structure that is usually assumed for both the liquid fraction calculation and the determination via conductivity measurements is strongly modified when large insoluble aggregates are present in the system. In this view, the method based on the liquid fraction determination through the measurement of the front propagation velocity seems to be the most suitable for studying the drainage of colloidal dispersion because of the lower dependence of this approach toward hypothesis on the local geometry of the foam continuous phase.

On the Spreading of Partially Miscible Liquids.

As time proceeds, partially miscible liquids spread as a cap surrounded by a primary film according to power laws, t(n), for both the leading edge (front) and the central cap. The corresponding exponents depend on the thickness, H, of the liquid aqueous substrate and the deviation of concentration from its saturation value, DeltaC=C-C(sat). As long as H is thick enough, here H>/=5 mm, the exponents are n=1/2 and n=1/3 for the front and the central cap, respectively. For thinner layers, H approximately 2 mm, and moderate DeltaC, the spreading is drastically hindered and the measured values can go down to n=0.1, due to the additional friction imposed by the confinement of the convective cells generated by dissolution below the primary film which anchor on the solid surface beneath the liquid substrate. Copyright 2001 Academic Press.