Time evolution of aqueous foams: drainage and coarsening
TL;DR: In this paper, the roles of bubble size, surface and bulk rheology and liquid fraction in free-drainage experiments were investigated. And the results showed that changing these foam parameters can induce transitions between different drainage regimes.
Abstract: We report new results on drainage and coarsening of aqueous foams. We show that these two effects can strongly interfere, enhancing the drainage velocity. Without coarsening, we have performed free-drainage experiments, in which local drainage rates are measured by electrical conductivity and by light scattering techniques. We have investigated the roles of the bubble size, of the surface and bulk rheology and of the liquid fraction. The results show that changing these foam parameters can induce transitions between different drainage regimes. The results are analysed in terms of two dimensionless numbers describing the balance between surface and bulk dissipation.
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TL;DR: This review covers recent advances in the study of foam drainage and coarsening, focusing especially on the effective role of the foam chemical components on those aging processes, and summarizes how the surfactant, the liquid bulk properties, and the gas modify or not the drainage andCoarsening features.
Abstract: This review covers recent advances in the study of foam drainage and coarsening, focusing especially on the effective role of the foam chemical components on those aging processes. The determination of the relevant parameters controlling foam drainage and coarsening today remains a major issue: are the physical parameters (like bubble size and liquid fraction) sufficient to define a foam and to predict its evolution, or do the chemical components also matter? And if these foam components are important, one has to determine by which mechanisms, and which microscopic parameters involved in these mechanisms are eventually crucial. I report here recent experimental results, shedding light on these issues. It allows us to summarize how the surfactant, the liquid bulk properties, and the gas modify or not the drainage and coarsening features. The coupling between drainage and coarsening is also discussed, as well as the role of the experimental conditions (sample height, shape or foam uniformity).
319 citations
TL;DR: A review of experiments, numerical simulations and theoretical models concerning foam rheology can be found in this paper, where the authors briefly recall the basic physics and physicochemistry of foams.
Abstract: Liquid foams can behave like solids or liquids, depending on the applied stress and on the experimental timescale. Understanding the origin of this complex rheology which gives rise to many applications and which resembles that of many other forms of soft condensed matter made of closely packed soft units requires challenging theoretical questions to be solved. We briefly recall the basic physics and physicochemistry of foams and review the experiments, numerical simulations and theoretical models concerning foam rheology published in recent years.
258 citations
TL;DR: Whey protein isolate was heat-treated at 85 degrees C for 15 min at pH ranging from 6.0 to 7.0 in the presence of NaCl in order to generate the highest possible amount of soluble aggregates before insolubility occurred, and these aggregates exhibited the highest foamability and foam liquid stability.
Abstract: Whey protein isolate was heat-treated at 85 °C for 15 min at pH ranging from 6.0 to 7.0 in the presence of NaCl in order to generate the highest possible amount of soluble aggregates before insolubility occurred. These whey protein soluble aggregates were characterized for composition, hydrodynamic diameter, apparent molecular weight, ζ-potential, surface hydrophobicity index, activated thiol group content, and microstructure. The adsorption kinetics and rheological properties (E‘, ηd) of these soluble aggregates were probed at the air/water interface. In addition, the gas permeability of a single bubble stabilized by the whey protein soluble aggregates was determined. Finally, the foaming and foam-stabilizing properties of these aggregates were measured. The amount of whey protein soluble aggregates after heat treatment was increased from 75% to 95% from pH 6.0 to pH 7.0 by addition of 5 mM to 120 mM NaCl, respectively. These soluble aggregates involved major whey protein fractions and exhibited a maximu...
219 citations
TL;DR: In this article, the authors 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.
Abstract: Aqueous 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.
215 citations
TL;DR: This review focuses on the current knowledge regarding (i) the mechanisms governing foamability and foam stability, and (ii) models for the foam column kinetics, and critically review and summarize the models that describe macroscopic foam behaviors within the context of the mechanisms involved.
206 citations
References
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01 Jan 1999
TL;DR: In this article, the shape of single soap movies and bubble clusters is discussed, as well as the condUCTIVITY FORMULA of LEMLICH and PHYLLOTAXIS.
Abstract: PREFACE APPENDICES A. THE SHAPE OF SINGLE SOAP FILMS AND BUBBLES B. THE THEOREM OF LAMARLE C. BUBBLE CLUSTERS D. THE DECORATION THEORUM E. THE CONDUCTIVITY FORMULA OF LEMLICH F. THE DRAINAGE EQUATION G. PHYLLOTAXIS H. SIMULATION OF LIQUID FOAMS I. BIBLIOGRAPHY APPENDICES
1,275 citations
TL;DR: In this paper, a new experimental method is presented using fluorescein dye to determine the spatial and temporal variations of the liquid volume fraction in aqueous foams This method was used for quantitative studies of liquid redistribution (drainage) in three types of experiments: forced, free, and pulsed drainage Characteristic quantities, such as the drainage velocity, show power-law dependences on experimental parameters that are inconsistent with traditional foam drainage models based on Poiseuille-type flow in the liquid-carrying channels (Plateau borders) of the foam.
Abstract: A new experimental method is presented using fluorescein dye to determine the spatial and temporal variations of the liquid volume fraction in aqueous foams This method is used for quantitative studies of liquid redistribution (drainage) in three types of experiments: forced, free, and pulsed drainage Characteristic quantities, such as the drainage velocity, show power-law dependences on experimental parameters that are inconsistent with traditional foam drainage models based on Poiseuille-type flow in the liquid-carrying channels (Plateau borders) of the foam To obtain a theoretical description, the foam drainage equation is generalized using an energy argument which accounts for viscous dissipation in both the channels and the nodes (or vertices, which are the junctions of four channels) of the liquid network Good agreement with results for all three types of drainage experiments is found when using this new model in the limit where the dissipation is dominated by the nodes
360 citations
TL;DR: In this paper, the authors review the history and recent development of this theory, analysing various exact and approximate solutions and relating them to each other, and propose a nonlinear partial differential equation for the foam density as a function of time and vertical position.
Abstract: The drainage of liquid in a foam may be described in terms of a nonlinear partial differential equation for the foam density as a function of time and vertical position. We review the history and recent development of this theory, analysing various exact and approximate solutions and relating them to each other.
283 citations
TL;DR: Free-drainage experiments with slow- and fast-coarsening gases show markedly different dynamics and elucidate the importance of the coupling of the two effects.
Abstract: The evolution of a foam is determined by drainage flow of the continuous (liquid) phase and coarsening (aging) of the dispersed phase (gas bubbles). Free-drainage experiments with slow- and fast-coarsening gases show markedly different dynamics and elucidate the importance of the coupling of the two effects. Strong coarsening leads to drainage times that are shorter (accelerated drainage) and independent of the initial liquid content (self-limiting drainage). A model incorporating the physics of both drainage and diffusive coarsening shows quantitative agreement with experiment.
241 citations
TL;DR: In this article, a theoretical model for interstitial liquid flow in a stationary or moving foam was devised by relating the physical structure of the foam to the physical properties of the surfactant and the foam movement.
Abstract: A theoretical model for interstitial liquid flow in a stationary or moving foam was devised by relating the physical structure of the foam to the physical properties of the surfactant and the foam movement. This was accomplished through a differential momentum balance within a typical capillary (Plateau border) of noncircular cross section with finite surface viscosity at its boundaries. Velocity profiles were then calculated and integrated numerically for the randomly oriented capillaries so as to obtain the overall liquid flow through the foam in terms of the pertinent variables. Results are presented in a form suitable for estimating concentrations and flow rates of product and waste streams in foam fractionation.
222 citations