Aqueous foams are studied both as materials with many applications, and as model systems for fields ranging from metallurgy to mathematics to biology. They are complex fluids with unique and unusual properties, exemplified as much by their multiscale structure as by the dynamical processes through which they evolve and even their dual liquid-like and solid-like behaviour. In this book, readers can easily find clear, up-to-date answers to their questions regarding the physical and physico-chemical properties of aqueous foams, explained using current knowledge of their structure, their stability, and their rheology. Newcomers to the field will find descriptions of numerous applications of foams in daily life and in industrial processes, the definition of basic concepts, hundreds of figures, and simple experiments to perform at home. Those who want to proceed further will find updated references, exercises with solutions, appendices with experimental and numerical techniques, and boxed text with the further mathematical detail.

Regular micro-porous polymeric membranes have recently been discovered by rapidly evaporating a solution of CS2 containing poly(p-phenylene)-block-polystyrene [1]. 1,2-dichloroethane (a chlorated solvent in which polystyrene gel phase has never been observed) is also found to produce ordered structures, which definitively excludes eventual effect of the gelation process during the membrane formation. The observation of the solution surface during the solvent evaporation reveals the growing of micron-sized water droplets trapped at the surface and forming compact aggregates. The study of the solution/water interface shows that the water droplets profile is in agreement with the pore shape observed in the membranes. Moreover, the copolymer was found to precipitate at the interface, forming a layer encapsulating the droplets and preventing their coalescence. In that way, the final structure results from the droplets stacking under the action of large surface currents. Finally, we argue that the decisive element in the formation of ordered structures is the ability of the polymer to precipitate at the solution/water interface, which seems to be related the star-polymer microstructure.

International audienceAqueous foams are complex fluids composed of gas bubbles tightly packed in a surfactant solution. Even though they generally consist only of Newtonian fluids, foam flow obeys nonlinear laws. This can result from nonaffine deformations of the disordered bubble packing as well as from a coupling between the surface flow in the surfactant monolayers and the bulk liquid flow in the films, channels, and nodes. A similar coupling governs the permeation of liquid through the bubble packing that is observed when foams drain due to gravity. We review the experimental state of the art as well as recent models that describe the interplay of the processes at multiple length scales involved in foam drainage and rheology

The effects of viscosity on the mechanical response of a liquid bridge are investigated in the case of small amounts of liquid axially strained between two moving spheres. An experimental setup allows the measurement of capillary and viscous forces exerted on the spheres as a function of the spheres separation distance and the spheres velocity. The experimental results are found to be accurately described over a large range in spheres velocity and liquid viscosity by a simple closed-form expression. In addition, the bridge rupture distance is found to increase like the square root of the separation velocity. Copyright 2000 Academic Press.

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Porous polymer films with a regular arrangement of pores (see figure) with a narrow pore size distribution have recently been reported. The preparation of the films from a variety of star polystyrenes, micellar polystyrenes, and block copolymers, the mechanism of formation, and the potential applications of the materials are presented .

This paper deals with the removal of a small sphere initially attached to a liquid interface. The sphere is small enough (0.3−1 mm) for the capillary force to dominate the interaction and large enough for the line tension effect to be negligible. We have measured simultaneously the force and the geometric parameters of the system as a function of the relative (sphere/interface) separation distance during the detachment process, with a high precision. This procedure allows us to quantify the effect of the contact angle hysteresis during the detachment process with respect to the force−path curve. It is shown that the previous work, which assumes a constant receding contact angle, does not describe our experimental data when the hysteresis effect dominates. By analytical integration of the capillary force experienced by the sphere during the detachment process, the first closed-form analytical expression for the detachment work was obtained. Comparison with our experimental data and with the existing numerical calculations showed good agreement. The effect of contact angle hysteresis on the detachment work is also quantified.

The stability of foam is investigated experimentally through coalescence events. Instability (coalescence) occurs when the system is submitted to external perturbations (T1) and when the liquid amount in the film network is below a critical value. Microscopically, transient thick films are observed during film rearrangements. Film rupture, with coalescence and eventual collapse of the foam, occurs when the available local liquid amount is too small for transient films to be formed. Similar experiments and results are shown in the two-bubble case.