Surface tension reduction effectiveness

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 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 ...

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. 

For both ionic and POE nonionics, as the temperature is increased, there is a decrease in both Ym and the CMC/C2o ratios. As a result, although the surface tension of the solution may be reduced to a lower value by increase in the temperature, the surface tension reduction effectiveness, IIcmc (= To — Ycmc> where y0 is the surface tension of the pure solvent at that temperature), is always reduced by increase in temperature. 

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. 

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 ... 

C2 / Ci =0.35, the system will exhibit antagonism in surface tension reduction effectiveness. 

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. 

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. 

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... 

A useful way to compare the surface activity of different surfactants is in terms of their efficiency and effectiveness [30]. Efficiency measures the surfactant concentration required to achieve a certain surface tension, while effectiveness is measured by the maximum reduction of the surface tension that can be obtained for that particular surfactant. In the following discussion these terms will be used in this specific defined sense. 

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. 

FIGURE 5-3 Surface tension-log C plot illustrating efficiency, —log C2o(pC2o), and effectiveness of surface tension reduction, IIcmc-... 

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. 

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... 

III.C. Synergism or Antagonism (Negative Synergism) in Surface or Interfacial Tension Reduction Effectiveness... 

At the point of maximum synergism or maximum antagonism in surface or interfacial tension reduction effectiveness, the composition of the mixed interfacial layer equals the composition of the mixed micelle, i.e., X E = the mole... 

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