Surface tension reduction surfactants

The log of the reciprocal of the bulk concentration of surfactant (C in mol/ L) necessary to produce a surface or interfacial pressure of 20 raN/m, log( 1 / On= 20 i e > a 20 mN/m reduction in the surface or interfacial tension, is considered a measure of the efficiency of a surfactant. The effectiveness of surface tension reduction is the maximum effect the surfactant can produce irrespective of concentration, (rccmc = [y]0 - y), where [y]0 is the surface tension of the pure solvent and y is the surface tension of the surfactant solution at its cmc. 

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

When ySB is reduced to the extent that ySB - Yso is negative, 6 will be larger than 90° and the soil can be completely removed by mechanical agitation in the cleaning bath. Although Ysb and you vary specifically with the use conditions, they can generally be correlated to the surface tension of the product solution [8], This surface tension is found to decrease with surfactant concentration up to the CMC, beyond which there will be no significant surface tension reduction. The surface tension reduction at CMC, defined as... 

In mixed sur-factant systems, the interactions betMeen sur-factants a-f-fects the tendency -for monolayer formation. At concentrations above the CMC, the surface tension may very slOMly increase or decrease. The surface tension at the CMC is close to the minimum surface tension which a surfactant system can attain. Therefore, in terms of surface tension reduction, the surfactant concentration required to attain a specified surface tension below the CMC and the surface tension at the CMC are indicative of the usefulness of a system. 

The conditions for synergism in surface tension reduction efficiency, mixed micelle formation, and Surface tension reduction effectiveness in aqueous solution have been derived mathematically together with the properties of the surfactant mixture at the point of maximum synergism. This treatment has been extended to liquid-liquid (aqueous solution/hydrocarbon) systems at low surfactant concentrations.) The effect of chemical structure and molecular environment on the value of B is demonstrated and discussed. 

Synergism in surface tension reduction efficiency. The efficiency of surface tension reduction by a surfactant is defined (9) as the solution phase concentration required to produce a given surface tension (reduction). Synergism in this respect is present in a binary mixture of surfactants when a given surface tension (reduction) can be attained at a total mixed surfactant concentration lower than that required of either surfactant by itself. This is illustrated in Figure 2. 

Figure 3 shows the total surfactant concentration required to attain a given surface tension (reduction) as a function of a in a number of binary surfactant systems. It illustrates the require-... 

Figure 3. Synergism in surface tension reduction efficiency for some binary surfactant mixtures.

Synergism in surface tension reduction effectiveness. This exists when the mixture of surfactants of its cmc reaches a lower surface tension than that obtained at the cmc of either component of the mixture by Itself. This is illustrated in Figure 5. 

Figure 5. Synergism in surface tension reduction effectiveness. (Ycmc 2 Y°cmc or Y°cmC2). (l) Pure surfactant 1 ...

The adsorption of surfactants at the liquid/air interface, which results in surface tension reduction, is important for many applications in industry such as wetting, spraying, impaction, and adhesion of droplets. Adsorption at the liquid/liquid interface is important in emulsification and subsequent stabilization of the emulsion. Adsorption at the solid/liquid interface is important in wetting phenomena, preparation of solid/liquid dispersions, and stabilization of suspensions. Below a brief description of the various adsorption phenomena is given. 

Commercially, the production and use of surfactants is dominated by modified hydrocarbon-based chemicals. In a number of instances, however, a hydrocarbon-type surfactant will not provide the desired product attributes or performance and, in such cases, two options are presented. One involves reformulation of the product to accommodate a hydrocarbon-type surfactant and the other is the use of a fluorosurfactant. Fluorosurfactants behave typically as would a hydrocarbon type except that properties such as surface tension reduction are larger in magnitude. Furthermore, the presence of fluorine in the hydrophobic portion of the molecule causes them to differ from their hydrocarbon counterparts in more subtle ways that have commercial importance. An example of a difference would be the reduced dielectric constant or index of refraction of a fluorosurfactant compared to its hydrocarbon analog. While this maybe of no consequence when formulating cleaners, it most certainly exists in a number of electronics applications. 

A term to describe the aforementioned quotient is cohesive energy density (CED heat of vaporization/unit volume). To a first approximation, the lower the CED, the lower will be the surface tension and this is the source of the increased efficiency in surface tension reduction of fluorosurfactants versus hydrocarbon surfactants. Therefore, fluorosurfactants are often the choice for applications demanding ultimately low surface tension. Furthermore, fluorosurfactants are far less compatible with water than are hydrocarbon surfactants. This is the origin of the increased effectiveness compared to hydrocarbon surfactants. 

Nearly all of the treatment processes in which fluids are injected into oil wells to increase or restore the levels of production make use of surface-active agents (surfactant) in some of their various applications, e.g., surface tension reduction, formation and stabilization of foam, anti-sludging, prevention of emulsification, and mobility control for gases or steam injection. The question that sometimes arises is whether the level of surfactant added to the injection fluids is sufficient to ensure that enough surfactant reaches the region of treatment. Some of the mechanisms which may reduce the surfactant concentration in the fluid are precipitation with other components of the fluid, thermally induced partition into the various coexisting phases in an oil-well treatment, and adsorption onto the reservoir walls or mineral... 

Air consists of molecules that are mainly non-polar. Surface tension reduction by surfactants at the air-aqueous interface occurs due to adsorption of surfactants at the interface, with the hydrophilic end of the surfactant oriented toward the liquid. The presence of the surfactant molecules reduces the net inward pull toward the bulk liquid, and therefore reduces the surface tension. 

Zonyl [Du Pont], TM for a fluorosurfactant wetting agent that is superior to hydrocarbon surfactants because of greater surface tension reduction. 

Amphiphiles (surface-active compounds or surfactants) are characterized by a molecular structure with both hydrophilic and hydrophobic domains. They tend to adsorb to surfaces and interfaces, with a concomitant lowering of surface tension. At the critical micellar concentration (CMC), the limit of surface tension reduction is reached and a spontaneous self-assembly takes place with the formation of aggregates (micelles). The size and structure of the micelles depend on the type and concentration of surfactant(s) present. 

For surfactants that are being used above Tk, maximum reduction, for all practical purposes, is reached at the CMC. Since surfactants are normally used above their Krafft points, we restrict our discussion to that condition and consider maximum surface tension reduction to occur at the CMC. 

Some of these factors affect Ym and the CMC/C2o ratio in parallel fashion (i.e., they increase both or decrease both) some in opposing fashion. When the effects are parallel, we can readily predict the resulting change in the effectiveness of surface tension reduction when they are opposed, it is difficult to do so. Thus, increase in the length of the hydrophobic group in ionic surfactants has little effect on either Ym or the CMC/C20 ratio, and we can therefore expect that an increase in the length of the hydrophobic group will have little effect on their effectiveness of surface tension reduction. 

On the other hand, at constant POE content, an increase in the length of the hydrophobic group causes an increase in the value of Tm but an almost equal decrease in log CMC/C20. As a result, as in the case of ionic surfactants, there is very little change in the surface tension reduction effectiveness of POE nonionic with increase in the length of the hydrophobic group. 

The reduction of the tension at an interface by a surfactant in aqueous solution when a second liquid phase is present may be considerably more complex than when that second phase is absent, i.e., when the interface is a surface. If the second liquid phase is a nonpolar one in which the surfactant has almost no solubility, then adsorption of the surfactant at the aqueous solution-nonpolar liquid interface closely resembles that at the aqueous solution-air interface and those factors that determine the efficiency and effectiveness of surface tension reduction affect interfacial tension reduction in a similar manner (Chapter 2, Section IIIC,E). When the nonpolar liquid phase is a saturated hydrocarbon, both the efficiency and effectiveness of interfacial tension reduction by the surfactant at the aqueous solution-hydrocarbon interface are greater than at the aqueous solution-air interface, as measured by pC2o and IIcmc, respectively. The replacement of air as the second phase by a saturated hydrocarbon increases the tendency of the surfactant to adsorb at the interface, while the tendency to form micelles is not affected significantly. This results in an increase in the CMC/C2o ratio. Since the value of rm, the effectiveness of adsorption (Chapter 2, Section IIIC), is not affected significantly by the presence of the saturated hydrocarbon, the increase in the... 

Indicate, in the table below, the effect of each of the following changes on the surface tension reduction effectiveness IIcmc of the surfactant in aqueous solution. Use symbols + = increase — = decrease 0 = little or no effect = effect not clearly known. 

In high-speed spray cleaning, a critical factor is the dynamic surface tension reduction of the surfactant solution (Chapter 5, Section IV), rather than its... 

It is apparent from condition 1 that synergism in surface tension reduction effectiveness can occur only when the attractive interaction between the two surfactants in the mixed monolayer at the aqueous solution-air interface is stronger than that in the mixed micelle in the solution phase. When the attraction between... 

Surfactants C and D of Problem 2 individually reduce the surface tension of an aqueous 0.1 M NaCl solution to 30 dyn/cm when their respective molar concentrations are 9.1 x 10 4 and 3.98 x 10-4. The mixture of them at a = 0.181 in Problem 2 has a surface tension value of 30 dyn/cm when the total molar surfactant concentration is 3.47 x 10-4. Will a mixture of surfactants C and D exhibit synergism or antagonism in surface tension reduction effectiveness ... 

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