Drainage and deformation in, and diffusion of gas through the foam film are noticed as the basic factors affecting foaming. They are arranged in a table where the positive and negative contributions to the stability of foam are indicated. Dynamic nature of the foam film such as Gibbs-Marangoni effect, dynamic surface tension of expanding and contracting surface, and so-called surface transport play an important role in the elucidation of foam phenomena. Further, Ross' and Kulkarni's opinions proposed for the defoaming phenomena are examined and improved explanations are presented. Extension coefficient instead of Ross' spreading coefficient and rupture of foam film instead of Kulkarni's rupture mechanism of surface film of bulk solution are proposed. Distinction between foam inhibition and foam breaking is proved important, and both of these factors are inferred to be properly taken into account for the study of defoaming.
The studies on the “Disjoining pressure” are reviewed as one of the widely accepted major factors which stabilizes the liquid film from rupture by resisting against the thinning of the intervening liquid phase separating two other phases. Various components of the “disjoining pressure”, namely, those repulsive forces originated from the overlapping of two electrical diffuse double layers, the van der Waals interaction with negative Hamaker constant, the steric effect of adsorbed nonionic molecules, and the elastic effect of anchored liquid crystalline molecules at the interfaces, are introduced together with the corresponding methods of measurement.
Foams are dispersed systems of gas particles. The stability of the foams, however, is determined by the property of foam membrane. Foams should, therefore, be studied as membrane systems. In this paper, fundamental properties of the foams are discussed on the basis of the surface chemical behavior of the membrane systems. Besides very stable foams covered with solid films or bimolecular films, less stable foams as well as unstable foams are stabilized by the adsorbed monolayer of foaming agent. These foams are the more stable if the more of the foaming agent is adsorbed the more tightly. Antifoams are classified into foam breakers and foam inhibitors. The foam breaker acts upon the foams already formed, by spreading on the surface of the foam membrane. On the other hand, the foam inhibitor acts to prevent foaming by driving out the foaming agent from the surface of the foam membrane as the result of preferential adsorption.
The existing test methods for measuring foaming and antifoaming properties of liquids are reviewed. The foaminess of liquids strongly depends on the test method. A number of methods cover most aspects of foam formation and stabilization. According to the principal of the foam generation, the foaming methods have been classified into two groups ; static and dynamic. The foam stability are expressed in terms of defined parameter such as the lifetime of bubbles, bubble size distribution and the gradual transformation of foam film caused by drainage.
Mechanism and detergency of foam washing and concerning basic investigations are reviewed. The foam was formed by injecting air into surfactant solution. When soiled substrate is placed parallel to the foam progress, Plateau border slides on surface of soiled substrate and remove the soil into the Plateau border. When porous substrate is fixed vertically to the foam progress, liquid and air in the foam is absorbed separately into the substrate, and foam is formed again from the porous substrate by the pressure of foam flow. Then the soil in the porous substrate is carried outward. Especially the vertical foam washing shows good detergency. The concerning basic investigations are dynamic action of single foam film, foaming action from porous media, and measurement of liquid volume fraction of foam by electric capacitance method.
Various separation methods utilizing bubbles are briefly reviewed. The basic principles of ore flotation for several minerals such as sulfides, oxides, silicates and soluble salts are outlined. Problems associated with fine particles flotation are discussed in connection with the separation between hematite and silica. An example of the application to municipal weste treatment is also included. Some of the experimental results concerning ion flotation, precipitate flotation, adsorbing particle flotation and microflotation, as applied to water treatment are presented. Attachment between particles and bubbles are discussed, in which particular attention is given to the dynamic double-layer effect around moving bubbles and adsorbed layer effect.
Foaming profile differs from one application to others due to the many variables relating to the foaming phenomena such as chemicals in the system, physical and mechnical conditions. Therefore, discussing defoaming or antifoaming exhibits much more complexity than the simple act of foaming. Due to the sheer complexity concerned, the actual technology seems to precede scientific understanding. In a wide range of industries, silicone antifoams are the most effective antifoams in both aqueous surfactant systems and nonaqueous systems. The efficiency can be explained by the surface chemical characteristics of the silicone polymer, which are derived from its unique structure such as backbone flexibility and low intermolecular forces, especially for polydimethylsiloxane. In this paper, defoaming by polysiloxane polymers is explained by the surface chemical nature of the polymer. As well, in aqueous systems, enhanced defoaming by compounding hydrophobic silica is explained by dewetting mechanisms based on previous theories.
Prinary benefit to personal washing products ; toilet soap, hair shampoo, body shampoo, facial cleanser etc. is just to remove soil on skin or hair. Recently, from the viewpoint of human science, safer washing agents for maintaining healthy skin and hair are becoming popular. On the other hand, for the user's viewpoint, good lather has clear and perceivable advantages in performance of washing products. Important performance of foam's character and it's evaluating method in toilet soap and hair shampoo are reviewed.
For aerosol foam cosmetic development, very careful selection of foam properties is essential. Hard, moist and uncollapse properties are preferable for shaving foam products. Soft, slightly dry and collapse properties are preferable for hair styling foam products. The influence of various components, fatty acids, alcohols, polymers, surface active agents, and propellants on foam properties is discussed.
Imitation whipping cream consists of water, fats, emusifiers, and diary products. It is commonly used for fillings and toppings for confectionery. Air is introduced through aeration or agitation of the cream and a structure in which many air bubbles are dispersed throughout the cream is built up. The foaming mechanism and the structure of whipped cream have been considered very interesting phenomena and have been studied for the past thirty years. However, ideas on the structure of whipped cream differ significantly. In this study, the effect of constituents such as fats, emulsifiers, and dairy products on the foaming properties are reviewed, and then the structure, the foaming mechanism, and the stability of the air bubbles in whipped cream are discussed.
The antifoaming agents in general use are silicone and polyoxyalkylene derivatives, and vegetable oil and animal oil derivatives. In the fermentation industry, the major antifoaming agents are polyoxyalkylene derivatives. The reason for this and uses of antifoaming agents are discussed in the following.
Cake batter and baked cake are complicated emulsions, and they may be defined as a multicomponent, heterogeneous dispersed system. Cake batter can be considered as a mixed colloidal system of a foam, an emulsion, and a suspension with an air content of 60 to 75 % by volume. Moreover, baked cake can be considered as a solid foam with an air cell content of 75 to 85 % by volume. The foam structure of cake batter is dynamically converted to the porous structure of baked cake during baking and it is therefore important to understand the role of foam structure of cake batter and baked cake. Recent researches revealed that the cake system is holistically understood as the interaction between the dispersed and the continuous phase. The colloidal aspects of cake production, baking mechanism and cake quality are reviewed as followed. (1) Foam formation in the cake batter (2) Foam structure changes during baking (3) Porous structure and cake quality
Antifoaming properties of lubricating oils are reviewed. There are two types of foaming in lubricating oils. One is surface foaming and another is air bubbles in oils. Surface foaming causes overflow of the oil from the reservoir, and air bubbles in oils promote cavitation erosion and wear brought about breakdown of oil film by bubbles. Usually antifoaming agents are added into lubricating oils. However, effects of antifoaming additives are influenced by base oils and other additives or mixing methods. In this review, effects of these several factors on antifoaming properties are summarized.
Foaming is one of major problems in the paint and ink industry. The need for controlling foaming is increasing with the advance of coating formulations from solvent based to water based. Using anti-foaming agents (defoamers) is the most popular way to remedy foaming problems. In this introduction, we report general and practical aspects of anti-foaming agents.
The formation of foam may cause many problems in the synthetic latex production, after the onset of synthetic latex production, many processes have been developed to prevent the formation of foam. In this review, several examples in the synthetic latex production by emulsion polymerization are described.
The effect of foam, especially of entrained air in stock suspensions, has received considerable attention in the paper industry. Air in stock has undesirable effects on both the operating efficiency of paper machines and the quality of the paper produced. Papermakers try to minimize foam generation by proper operation and mechnical means. However, complete avoidance of air entrainment is almost impossible, and antifoams have become indispensable processing aids for papermaking. The purpose of this paper is to review the practical effects of foam on papermaking and to discuss the typical antifoams widely used in the paper industry.
Various foaming problems concerned with the wet-processing in textile industries and procedures to control the foaming troubles are discussed. The choice of antifoaming agents and foamless surfactants is a critical problem. On the contrary, the positive application of foam in the field of textile finishing has bright prospects for the future, because it should give us a lot of profits in the energy saving and solves the pollution problems in the textil mills. The characteristics of foam used in the continuous process such as sizing, preparation, mercerization and resin-finishing are discussed. Furthermor foaming-agents and continuous foam generators are reviewed.
Waster-papers are recycled by deinking.All over the world, the flotation method is the main stream as the deinking method. In the flotation method, air bubbles are introduced into the pulp slurry continuously, and removed ink particles are adsorbed on the air bubble and rejected out. There are three particles, namely, cellulose ink, and bubble, and main four interaction between them in the flotation cell as mentioned below. The following relationship must be held to remove the ink particles effectively. Vr0<Vr1<<Vr2<Vr3 where Vr0, Vr1, Vr2 and Vr3 are the repulsive energy between ink-ink, ink-bubble, ink-cellulose and cellulose-bubble, respectively.
Autoclaved lightweight aerated concrete (ALC), which has outstanding fire resistance, heat insulation, lightness and strength, is widely used as a superior material for homes and multistory buildings in Japan. It is produced by a two-step molding and autoclaving process, using quartz, lime, portland cement and small quantities of aluminum as raw materials. In the molding step, aluminum reacts with alkali to generate hydrogen gas, thus forming “air pores” in the slurry, while calcium silicate hydrates are produced by the reaction of lime, portland cement and water with voids forming in the interparticle spaces vacated by the reacting water. In the autoclaving step, tobermorite (crystalline calcium silicate hydrates) is formed by the reaction of quartz and calcium silicate hydrates under high temperature, high pressure steam, and the interparticle voids are reduced to “micropore” size as a result of the hydrothermal reaction. The air-pore and micropore structure adds unique physical properties to the ALC.
In many wastewater treatment plants, foaming occurs and it causes serious problems. Soddel and Seviour (1990) reviewed the microbiology of foaming in activated sludge plants. It has been found that specific microbial species, Nocardia amarae, N. pinensis, Rhodococcus sp. and Microthrix parvicella are dominant in the stable foams. The gas bubbles, hydrophobic particles and surfactants are required for foam formation. Controlling factors in plant operation involve temperature, oxygen content, grease and oil content, sludge age etc. Various methods have been applied to prevent foaming. Selective flotation utilizes the property of foam forming microbes. Mechanical foam-breaking systems include water-sprays, vacuum systems and foam breaking systems. Effective antifoams have been used to break foams and prevent foaming. They are organic antifoams and silicone products.
Dry chemicals and inert gases are generally used as fire extinguishants to extinguish small-scale flammable fuel fires such as oil spill fires and oil stove fires. But they are not suitable for extinguishing large-scale oil fires, because of the following three reasons ; 1. there is a possibility of reignition after the fire extinction. 2. it costs much when they are applied continuously for a long time. and 3. the largest drawback is that these agents do not prevent the fuel vaporization after the fire extinction. On the other hand, no fire-fighting foams have such drawbacks. They are sure extinguishants for fires, of chemical plants, large fuel storage tanks and of major oil spills. Medium and high expansion foams for fire suppression are commercially available as well as convensional low expansion-type foams. Synthetic surfactant, fluorinated surfactant and fluoroprotein foams have been developed one after another, although there are still conventional hydrolized keratin-protein foams available. These newly developed foams have found a way to a practical application in the fire-fighting field. This paper describes state of the art of fire-fighting foams and explains the details of each foam.
Ion flotation method for the preparative sample treatment before chemical measurements was reviewed. Ion flotation is an adsorptive bubble separation technique. It is based on the fact that surface active materials have the property of adsorption on the surface, in this case, gas-liquid interface. The method could be applied when 1) the solute to be measured become easily surface active after reacted with a complexing agent or else, 2) the formation of ion pair between the solute and a surface active agent is possible. In this paper, typical examples were shown to understand the variety of the methods. They are collective separations of metal ions using complexing agents and surfactants, those of anions through derivatizing them to be hydrophobic, and the solvent sublation method, in which the solvent put on the sample solution extracts the ion pairs coming up with the bubbles. Further, a new method for the selective collection of solutes using surface active cyclodextrin which has the capability of molecular recognition was proposed with preliminary results.