Surface tension Reduction

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... 

Table VIII shows that G, L-A and S residues cause the same degree of increase in the cmc and only slightly affect surface tension reduction and molecular area on the adsorption film. For each series of this type of nonionic, plots of log cmc vs. number of carbon atoms(8 - 16) in the acyl chain gave a straight line with a slope similar to that for the usual type of nonionic. However, the former types differ distinctly from the latter type in...

Although the efficiencies of surface tension reduction, pCao, for the betaines and their corresponding sulfobetaines are almost the same, the former appear to show greater effectiveness in surface tenion reduction, as indicated by the values. This may be due... 

As for other types of fluid particle, the internal circulation of water drops in air depends on the accumulation of surface-active impurities at the interface (H9). Observed internal velocities are of order 1% of the terminal velocity (G4, P5), too small to affect drag detectably. Ryan (R6) examined the effect of surface tension reduction by surface-active agents on falling water drops. 

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 2. Synergism in surface tension reduction efficiency (Ci2 < C ° or 2°) or in mixed micelle formation...

C,-. , required to attain a given surface tension (reduction) is... 

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-... 

Table I. Synergism in Surface Tension Reduction Efficiency ...

By mathematical treatment similar to that for synergism in surface tension reduction efficiency, we have found that the conditions for synergism in mixed micelle formation are ... 

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 ...

For solutions of AEg with different distributions of hydrocarbon chain lengths, the Y log C curves appear to be different than mono-component system. The surface pressure at critical micelle concentration (iTcjic) AEg with a long hydrocarbon chain (C gEg) is Increased by adding the short AEg, but the effect is not significant if the hydrocarbon chain is in a wide distribution (i.g. coconut fatty radical) (Figure 2,3,4). As for the efficiency of surface tension reduction there is a synergestic effect for the mixed... 

By contrast, Fox and Bala (23) observed that the degree of surface tension reduction was dependent on the amount of carbon source (potato) initially present in the medium. 

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. 

Figure 2 illustrates how the tailor-made silicones function as IMR agents in RIM molding. Due to the known surface tension reduction phenomenon of silicone fluids in urethanes and the differences In surface tension at the urethane/mold interface, internal mold release agents based upon silicone molecules can be developed to selectively migrate at different rates to the urethane/mold interface. There, it will orientate itself to build a protective layer which decreases the ability of the urethane to wet-out the mold surface. The inability of the urethane to wet-out the mold surface will facilitate release. 

Use Wetting agent, surface-tension reduction, detergent. 

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. 

The paraffin chain radical is hydrophobic and the solubility of the alcohol is merely due to the hydrophilic OH-groups. It is known, that the surface tension reduction by organic substances decreases with increasing chain... 

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