Foam, advantages Surfactant

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 advantages of alkyl A -methylglucamides as surfactants are similar to those of APGs . They are based on renewable resources, and are high-foaming, mild surfactants that emulsify well. 

Quick-breaking foams consist of a miscible solvent system such ethanol (qv) [64-17-5] and water, and a surfactant that is soluble in one of the solvents but not in both. These foams are advantageous for topical appHcation of pharmaceuticals because, once the foam hits the affected area, the foam coUapses, deUvering the product to the wound without further injury from mechanical dispersion. This method is especially usehil for treatment of bums. Some personal products such as nail poHsh remover and after-shave lotion have also been formulated as quick-breaking foams. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

Alcohol sulfates (AS) are usually manufactured by the reaction of a primary alcohol with sulfur trioxide or chlorosulfonic acid followed by neutralization with a base. These are high foam surfactants but they are sensitive to water hardness and higher levels of phosphates are required. This latter requirement has harmed the market for this type of detergent, but they are 2% of production for the major household surfactant market. Sodium lauryl sulfate (R = Cn) is a constituent of shampoos to take advantage of its high-foaming properties. 

One advantage of using a cleavable acetal surfactant instead of a conventional amphiphile has been elegantly demonstrated in a work by Bieniecki and WUk [51]. A cationic 1,3-dioxolane derivative was used as surfactant in a microemulsion formulation that was employed as a reaction medium for an organic synthesis. When the reaction was complete, the surfactant was decomposed by addition of acid and the reaction product easily recovered from the resulting two phase system. Through this procedure the problems of foaming and emulsion formation, frequently encountered with conventional surfactants, could be avoided. 

This brief review has attempted to discuss some of the important phenomena in which surfactant mixtures can be involved. Mechanistic aspects of surfactant interactions and some mathematical models to describe the processes have been outlined. The application of these principles to practical problems has been considered. For example, enhancement of solubilization or surface tension depression using mixtures has been discussed. However, in many cases, the various processes in which surfactants interact generally cannot be considered by themselves, because they occur simultaneously. The surfactant technologist can use this to advantage to accomplish certain objectives. For example, the enhancement of mixed micelle formation can lead to a reduced tendency for surfactant precipitation, reduced adsorption, and a reduced tendency for coacervate formation. The solution to a particular practical problem involving surfactants is rarely obvious because often the surfactants are involved in multiple steps in a process and optimization of a number of simultaneous properties may be involved. An example of this is detergency, where adsorption, solubilization, foaming, emulsion formation, and other phenomena are all important. In enhanced oil recovery. 

Because the sarcosinates have the ability to raise the cloud point of nonionic surfactants, this feature can be used to advantage in the formulation of dishwasher rinse aids. At the cloud point and up to 15C above it, foam generation is reduced and detergency is enhanced. By adjusting the cloud point of the formula to the use temperature, one can take full advantage of this performance feature. 

Synthetic surfactants are commonly used in shampoos, sometimes for reasons of cost and sometimes for performance. Non-ideal mixing in micelles can result when the repulsions between different surfactant head-groups are not uniform, such as when an anionic sulfonate is mixed with a non-ionic ethoxylate or when an anionic is mixed with a betaine. This causes the cmc of the mixture to be smaller than would be the case for ideal mixing, or for either surfactant alone. Such a reduction in cmc can be used to reduce the surfactant monomer concentration in a shampoo. This is an advantage since reducing the monomer concentration reduces the amount of eye and skin irritation experienced when the shampoo is used [904], Other synthetics offer other benefits. For example, some silicone surfactants can not only function as emulsifiers in hair and skin care products, but also act to improve feel, gloss, sheen, emolliency, conditioning and foam stabilization [905]. 

Ethoxylation is carried out in the same manner as for primary alcohols described earlier but, in general, only up to the 3-mol ethoxylate as a feedstock for some specialised ether sulphates. These products show some advantages in wetting and foaming applications compared to the straight alcohol sulphates. These twin tail surfactants require less co-surfactant to make microemulsions and emulsify 3-5 times more oil than sulphates made from linear hydrophobes. 

The cationic surfactant reduces the capillary forces already at concentrations far below the erne. This may be a great advantage since problems occurring at concentrations around the cmc like melting of the photoresist structures [15] or defect creation by foaming [17] can be avoided. 

A great advantage of the cationic surfactant rinse is that the minimum of the capillary forces is obtained already at concentrations far below the erne. Low amounts of surfactant are needed and problems as melting of the structures or foaming occurring at high surfactant concentration are avoided. 

The quantity xp is a much better defined characteristic of foam stability (since the pressure in the borders along the height of the foam column remains constant during its destruction). This parameter is also much more sensitive to the kind of surfactant, electrolyte concentration and other additives, compared to the lifetime of the foam in gravitational field, with an averaged pressure value from 0 to pgH. Estimation of the stability of foams from different surfactants by xp and by the Ross-Miles test has been reported in [16]. The results are discusses in Section 7.6.1. The advantages of the Foam Pressure Drop Technique and, respectively, xp as a characteristic of the foam stability, are clearly shown. 

These two examples with the homologous series of alkylsulphonates and alkylsulphates indicate the undoubted advantages of Foam Pressure Drop Technique for determining the foam stabilising properties of surfactants. This technique allows to distinguish small differences in the foam stabilising ability of surfactants. 

Though not quantitative, the comparison between the two techniques provides information about the effect of the pressure in the foam liquid phase as well as the effect of the foam film type. The advantages of the Foam Pressure Drop Technique for estimating the foam stabilising ability of the surfactants is indisputable. 

In the meantime, the significant advantage indicated by our laboratory work for injection of carbon dioxide as a foam or emulsion rather than alternately with water (WAG) will, we hope, serve as a stimulus to the oil companies carrying out carbon dioxide floods to give consideration to this version of the process. Many of these companies have the Todd, Dietrich and Chase Multiflood simulator, or one which is similar. The option to precipitate or adsorb a component is necessary. Then the surfactant component can be adsorbed and can also provide a higher viscosity when it is not adsorbed (simulating foam). 

A sorption colloid flotation method has been developed for the separation of vanadium from sea water. The separation is based on a surfactant-collector inert gas system in which vanadate is sorbed on a positively charged colloidal iron(III) hydroxide collector. The vanadate enriched collector rises to the sea water surface and floats as a separable foam with aid of sodium dodecylsulfate as surfactant and nitrogen as inert gas. The major advantages of this method are the rapid attainment of flotation and the excellent recovery of 86 % vanadium based on spiked sea water samples. Flotation was found to be highly pH sensitive optimal values were found to be 5.00 + 0.02. In effect, at pH 4.90 a slight decline in recovery of vanadium could already be observed, whereas at pH 7 and above there was no vanadium float 53). 

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