Critical micelle concentration foams

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. 

If one compares several commercial LAS samples for foam stability, detergency performance, critical micelle concentration (CMC), hardness sensitivity, or... 

Schulze [51] described an extensive study on C12-C14 ether carboxylic acid sodium salt (4.5 mol EO) in terms of surface tension, critical micelle concentration (CMC), wetting, detergency, foam, hardness stability, and lime soap dispersing properties. He found good detergent effect compared to the etho-xylated C16-C18 fatty alcohol (25 mol EO) independent of CaCl2 concentration, there was excellent soil suspending power, low surface tension, and fewer Ca deposits than with alkylbenzenesulfonate. 

The foaming propensity of surfactants generally reaches a maximum at the critical micelle concentration, beyond which there appears to be little further contribution to foam density. Foam stabilisers are also added in some cases. The two important steps in the foam treatment of textile materials are generating the foam and applying it to the substrate ... 

Choose nonionics as suds stabilizers for use with foaming surfactants that are ionic. Prefer those with higher ability to lower the critical micelle concentration (CMC) of the foaming surfactant. 

Test Methods. Surface tension (y) measurements were taken by Wil-helmy method (25+0.1°C). Critical micelle concentrations (cmc) were obtained from Y logC curves. Contact angle. Type GI, Japan. Wetting test. Canvas disk method, CIS,HG-2-380-66. Foam test, Ross-Miles lather method. Emulslbillty was determined by mixing 20 ml of 2.5%... 

The great majority of anionic surfactants will generate significant foaming in solutions above their critical micelle concentration (CMC), which is a desirable attribute in most cleansing applications, but can restrict the use of anionic surfactants in areas where foam is a problem. 

Correlation equations relating surfactant chemical structure to performance characteristics and physical properties have been established. One atmosphere foaming properties of alcohol ethoxyl-ates and alcohol ethoxylate derivatives have been related to surfactant hydrophobe carbon chain length, ethylene oxide content, aqueous phase salinity, and temperature. Similar correlations have been established for critical micelle concentration, surfactant cloud point, and surfactant adsorption. 

Surfactant critical micelle concentration (cmc) may be related to chemical structure using multiple correlation analysis. The cmc value plays an important role in surfactant adsorption, foaming, and interfacial tension properties. The 25 C cmc values of a series of high purity single component highly linear primary alcohol ethoxylates (Table 6) were analyzed using equation 4 ... 

For a surfactant that is present in a foam separation reactor at a concentration near or above its critical micelle concentration, the surface excess may be approximately a constant representing a completely saturated air-water interface ... 

The foam centrifuge compresses the primary foam (db > 1 mm) to a flowable secondary foam (db > 0.05-0.1 mm). Preliminary experiments showed that a foam density of ca. 0.5 kg/1 is necessary [533], which was attained with a rotor tip speed of ca. 20 m/s. A similar trend of the density of the compacted foam pf as a function of the rotor tip speed u was achieved with the foam turbine [171] for which a foam density of 0.35 kg/1 was sufficient for the secondary foam to flow. Fig. 4.26 shows these measurements for both types of foam breaker and different foams and also shows the large effect the concentration of the foaming agents exerts in the range 0.2-2.0 mmol/1 = 0.073-0.73 g/L (CMC is the Critical Micelle Concentration). However, Fig, 4.26 also shows that to realize the same flowability of the foam... 

From the plot of the values of IFT measured at different surfactant concentrations, such as shown in Figure 12, the critical micelle concentration (CMC) can be determined as the concentration at which the change of slope occurs. Figure 12 shows such a plot made at reservoir conditions in a particular field. The CMC is a useful reference concentration for a particular surfactant, although its full significance for foam formation and stability within porous media is not yet known. 

Retention in Porous Media. Anionic surfactants can be lost in porous media in a number of ways adsorption at the solid—liquid interface, adsorption at the gas—liquid interface, precipitation or phase-separation due to incompatibility of the surfactant and the reservoir brine (especially divalent ions), partitioning or solubilization of the surfactant into the oil phase, and emulsification of the aqueous phase (containing surfactant) into the oil. The adsorption of surfactant on reservoir rock has a major effect on foam propagation and is described in detail in Chapter 7 by Mannhardt and Novosad. Fortunately, adsorption in porous media tends to be, in general, less important at elevated temperatures 10, 11). The presence of ionic materials, however, lowers the solubility of the surfactant in the aqueous phase and tends to increase adsorption. The ability of cosurfactants to reduce the adsorption on reservoir materials by lowering the critical micelle concentration (CMC), and thus the monomer concentration, has been demonstrated (72,13). 

Bovine serum albumin (BSA), a globular protein, is often applied as a model protein for foam formation. The surface tension of BSA solutions as a function of time indicates that, depending on the BSA concentration, it can take 15 to 20 h to attain an equihbrium surface tension which is independent of the BSA concentration. The coagulation rates are shght and the loss of native protein in the svuface film due to adsorption and denaturation is compensated by the quick and continuous diffusive transport of native protein to the surface. Therefore, the critical micelle concentration (CMC) and Ocmc can be evaluated from these measmements. 

A foam is a dispersion of a gas in a liquid or a solid. The formation of foam relies on the surface activity of the surfactants, polymers, proteins, and colloidal particles to stabilize the interface. Thus, the foamability increases with increasing surfactant concentration up to critical micelle concentration because above critical micelle concentration, the unimer concentration in the bulk r ains nearly constant. The structure and molecular architecture of the foam is known to influence foam-ability and its stability. The packing properties at the interface are not excellent for very hydrophilic or very hydrophobic drug. The surfactant promoting a small spontaneous curvature at interface is ideal for foams. Nonionic surfactants are the most commonly used one. The main advantage with foams is its site-specific delivery and multiple dosing of the drug. ... 

The optimum concentration of surfactant for maximum foam effectiveness has to be determined empirically. It is often of the order of about 0.1 -0.3 mass% active surfactant. A useful starting point for preparing and/or testing foams is a surfactant concentration that is 1.5 - 2 times the value of the critical micelle concentration (cmc). 

For many of the applications noted in Table 3.2, the desired properties will vary significantly. For that reason, such characteristics as solubility, surface tension reducing capability, critical micelle concentration (cmc), detergency power, wetting control, and foaming capacity may make a given surfactant perform well in some applications and less well in others. The universal surfactant that meets all of the varied needs of surfactant applications has yet to emerge from the industrial or academic laboratory. 

There are several important physical and chemical parameters that characterize a surfactant and determine how it will perform in a dishwashing detergent. These parameters inclnde its critical micelle concentration, ability to pack at an air, oil, or solid interface, and ability to lower interfacial tension. Yet another important parameter is the extent to which varions snrfactants interact with each other to provide synergistic benefits. These fundamental characteristics determine how well the surfactant or snrfactant mixture will remove grease, how well it will foam, and even how irritating/mild it will be on hands. 

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