Foams reduced surface tension

In general, organic contaminants induce foaming and inorganics increase surface tension, although clearly there are exceptions. For example, sugar increases surface tension, while tannins, lignosulfonates, car-boxymethyl cellulose (CMC), phosphinocarboxylic acids (PCAs), and other dispersants reduce surface tension and help destabilize foams. 

Although many factors, such as film thickness and adsorption behaviour, have to be taken into account, the ability of a surfactant to reduce surface tension and contribute to surface elasticity are among the most important features of foam stabilization (see Section 5.4.2). The relation between Marangoni surface elasticity and foam stability [201,204,305,443] partially explains why some surfactants will act to promote foaming while others reduce foam stability (foam breakers or defoamers), and still others prevent foam formation in the first place (foam preventatives, foam inhibitors). Continued research into the dynamic physical properties of thin-liquid films and bubble surfaces is necessary to more fully understand foaming behaviour. Schramm et al. [306] discuss some of the factors that must be considered in the selection of practical foam-forming surfactants for industrial processes. 

A severe problem in ink performance is the presence of bubbles in the ink. Foaming is often observed in inks which contain surfactants and polymers. A common solution to this problem is addition of a defoamer, which is a molecule that causes breakdown of foam which is already present. The defoamers act by a) reducing surface tension... 

Foaming—Saponins, and other amphoteric compounds that reduce surface tension, exhibit a fairly characteristic tendency to form stable, persistent foams from aqueous alcohol solutions. 

Features Reduced tendency for orange-peei or cratering reduced surface tension with iittie or no foam formation Properties Coioriess ciear iiq. dens. 1.00-1.02 g/cm (20 C) fiash pt. 24 C 50-52% act. 12% NCO on act. ingreds. 

Surfactant ( )s9r- fak-t9nt [swr ce-active + -ant] (1950) n. Contracted from surface-active agents, these are additives which reduce surface tension and may form micelles and thereby improve wetting (wetting agents) help disperse pigments (dispersants) inhibit foam (defoamers) or emulsify... 

Dams RJ et al. (2009) Preparation of fluorinated ether compounds used to reduce surface tension, make foam, and treat surfaces. World Appl 2,009,071,5. 3M Innovative Properties Company, USA... 

Another effective method of acid diversion is the use of foams. Foam is a mixture of a liquid phase and a gas phase. A suitable surfactant is added to the liquid phase to reduce surface tension and stabilize foam lamellae. Nitrogen and carbon dioxide are exclusively used in the field to form foams [17]. The volume percent of the gas phase in the foam is known as foam quality (tx), and is calculated using the following equation ... 

Quite logically, new columns are developed to meet a real analytical need. Proliferation in the use of surfactants is a case in point Surfactants have both hydrophilic and hydrophobic centers and are widely used in many industries because of their abiUty to reduce surface tension. Anionic surfactants, classified as alkanesul-fonates, alkyl sulfates and alkylbenzenesulfonates, are commonly used in detergents, cleansing agents, cosmetics and hygienic products. Cationic surfactants are quaternary ammonium compounds, which are used in cosmetics, disinfectants, foam depressants, and textile softeners. Nonionic surfactants are also present in a... 

Carry-over can be caused by dirty wash liquid or particulates in the hydrocarbon feed. Caustic strengths in excess of 15%-20% can contribute to carry-overs. Extraneous chemicals that reduce surface tension (surfactants) and thus promote foaming are obvious culprits. 

These substances reduce surface tension in liquids. For example they stabilize the cells of polyurethane foams during the foaming process. 

Emulsions, as well as other hydrophobic colloids (such as foams), can be stabilised mechanically or by the addition of natural or synthetic surfactants called emulsifiers, which reduce surface tension at the interface of both phases. For example, the surface tension at the interface of oil-water is 20-25 mN/m. In the presence of monoa-cylglycerol (0.3%), it is reduced to about 80%, and by adding a mixture of lecithin and monoacylglycerol it drops to about 5% of the initial value or less. In the interface, lipophilic groups of the emulsifier molecule interact with the lipophilic (non-polar) molecules of oil and hydrophilic (polar) groups of the emulsifier interact with water. The emulsifier, for example phospholipid or monoacylglycerol, forms a protective barrier that prevents coalescence of oil drops, connects the two liquids (oil and water) and stabilises the emulsion (Figure 7.33). 

In summary, it can be stated that the foam abriity a given surfactant imparts depends on die surfactants effectiveness in reducing surface tension, its diffusion... 

Saponins have the ability to produce foam, when a water solution containing this type of actives is stirred. This action is due to their ability to reduce surface tension. Therefore, they are known as natural surfactants. Saponins also exert a haanolytic action, a characteristic of the triterpene saponins. A number of plants used in cosmetics can be cited in... 

Features Moderate foaming power reduces surface tension does not precipitate in the presehce of ions in hard water maintains chemical, physical stability in alkaline or acid environments compat. with non-ionic, anionic, cationic surfactants... 

The fluorinated surfactant-hydrocarbon surfactant mixtures have unique properties. In two-phase systems of water and a hydrocarbon solvent, the fluorinated surfactant reduces surface tension and the hydrocarbon surfactant decreases the interfacial tension. For example, an aqueous foam of mixed surfactants spreads on a hydrocarbon solvent because the fluorinated surfactant adsorbs preferentially at the air-water interface, whereas the hydrocarbon surfactant adsorbs at the water-oil interface (see Chapter 8, Fire-fighting Foams). 

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