Surface tension reduction values

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... 

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. 

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. 

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... 

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 ... 

For example, carbon atoms located on branch sites will contribute approximately two thirds as much to the character of a surfactant molecule as one located in the main chain (56). The above-mentioned surfactants [35a-h], [37a-h] follow this general trend. In addition, it has generally been found that the presence of alkyl groups attached to the nitrogen seems to have little effect on the surface tension reduction of a surfactant. This general trend also holds for the y values of the compounds [35a-h], [37a-h]. 

The time dependent surface tension decay was measured according to the drop-volume technique as outlined by Tornberg [18,19]. The automatization procedure according to Arnebrant and Nylander [20] was employed. In this method surface tension reduction by macromolecules during adsorption at the air-water interface is measured by formation of drops of certain volumes. Time for detachment of the droplets is recorded. Surface tension calculated [19, 20] was plotted against detachment time and the value attained after 2000 seconds was set as the equilibrium value. The surface tension of the solutions is still decreasing after this period of time, but the rate of decrease is small, less than 0.05 mNm" per 100 seconds. The maximum error in surface tension values is 1.5%. 

The first condition means that the two surfactants must have an attraction for each other the second that this attraction must be stronger than the difference between the natural logarithms of the two concentrations needed to produce this same surface tension (reduction) of the solvent. Therefore, to maximize this type of synergism, two materials with strong attraction for each other (large negative P° value) should be used. 

Anderson s group (Pino et al., 2009) studied the micellar properties of aqueous solutions of two ILs, l-hexadecyl-3-butylimidazolium bromide and 1,3-didodecylimidazolium bromide, in the presence of several organic solvents (methanol, 1-propanol, 1-butanol, l-p>entanol, and acetonitrile) by surface tensiometiy. For both ILs, increases in the cmc values and minimum surface area per surfactant molecule, decreases in the maximum surface excess concentration, adsorption efficiency and effectiveness of surface tension reduction were obtained when increasing the organic solvent content. 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

In the narrow tubes used by Beek and van Heuven, the bubbles assumed the shape of Dumitrescu (or Taylor) bubbles. Using the hydrodynamics of bubble rise and the penetration theory of absorption, an expression was developed for the total absorption rate from one bubble. The liquid surface velocity was assumed to be that of free fall, and the bubble surface area was approximated by a spherical section and a hyperbola of revolution. Values calculated from this model were 30% above the measured absorption rates. Further experiments indicated that velocities are reduced at the rear of the bubble, and are certainly much less than free fall velocities. A reduction in surface tension was also indicated by extreme curvature at the rear of the bubble. 

The values obtained in different laboratories for the activity of various electrocatalysts are not directly comparable. The reduction of oxygen — for which data have been published by various groups — proceeds at the three-phase boundary where gas, liquid, and solid meet. This boundary is affected by such macroscopic properties of the catalyst as particle size, density, surface tension, and porosity. 

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