Microgravity studies of aqueous wet foams.

Foams and foaming pose important questions and problems for both fundamental research and practical applications. Despite the fact that foams have been extensively studied, many aspects of foam physics and chemistry still remain unclear. Experiments on foams performed under microgravity can be extended far beyond their counterpart where gravity is fully present (i.

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.

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 %.

Liquid drainage through aqueous foam: study of the flow on the bubble scale.

Macroscopic properties of foams are highly dependent on the liquid volume fraction, which has motivated many studies on foam drainage in the last decade. Theoretical developments and recent experimental results have suggested that two macroscopic drainage regimes could be expected, in relation with flow transitions occurring at the microscopic level, essentially in the Plateau border channels. We have constructed a setup, the Plateau border apparatus, to study the hydrodynamics of a single Plateau border channel, focusing on the surface properties of the foaming solution.

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.

Topology of slightly polydisperse real foams.

The topology of slightly polydisperse, (meta-)stable, real foams was investigated by means of optical tomography associated with a numerical reconstruction procedure. The values of the mean numbers of faces per bubble and edges per face were very close to Matzke's data (1946). The real foams were essentially disordered and possessed a noncentered symmetry, and ideal structures also could not be observed.

The zeta-potential of the endogenous particles of a wine of Champagne in relation to the foaming behaviour.

It was shown that the endogenous particles of the champagnes influence the lifetime, and not the maximum expansion of their evanescent foam (Food Hydrocolloids (1999) 12, 217-226). Actually, champagnes are electrolytic solutions with pH 3 and ionic strength equal to 0.02 mol/l in which bentonites, diatomites, and yeast cells are the more numerous colloids and particles present.

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.

Influence of Dynamic Surface Tension on the Spreading of Surfactant Solution Droplets Impacting onto a Low-Surface-Energy Solid Substrate.

We have investigated the impact of single droplets of various surfactant solutions on a low-surface-energy solid substrate using a high-frequency visualization technique (one picture every 100 μs). Whatever the surfactant, the drop spreads and retracts in about 1 s under the action of inertia and capillarity, respectively. During retraction, the capillary waves can be amplified and, in some cases, even yield droplet bouncing.

Dissolution of a Drop on a Liquid Surface Leading to Surface Waves and Interfacial Turbulence.

If a droplet of liquid with a lower surface tension than that of water and partially soluble in water is deposited on a free water surface, it spreads, dissolves, and simultaneously creates surface tension gradients leading to Marangoni instability and interfacial turbulence. In a first stage, if the solubility of the drop is not too high, there is formation of patterns that evolve in time, eventually leading to interfacial turbulence and droplet disappearance. These patterns, which on occasion last quite long time intervals, result from the interaction and collision of surface waves sustained by the surface tension gradient.