Surface tension sulfate

As an example of the application of the method, Neumann and Tanner [54] followed the variation with time of the surface tension of aqueous sodium dode-cyl sulfate solutions. Their results are shown in Fig. 11-15, and it is seen that a slow but considerable change occurred. 

Ammonium lauryl sulfate is an anionic surfactant. This means it lowers the surface tension of water, making the water spread more easily. Surfactants are also called wetting agents—in plain terms, they make water wetter. 

The influence of the presence of alcohols on the CMC is also well known. In 1943 Miles and Shedlovsky [117] studied the effect of dodecanol on the surface tension of solutions of sodium dodecyl sulfate detecting a significant decrease of the surface tension and a displacement of the CMC toward lower surfactant concentrations. Schwuger studied the influence of different alcohols, such as hexanol, octanol, and decanol, on the surface tension of sodium hexa-decyl sulfate [118]. The effect of dodecyl alcohol on the surface tension, CMC, and adsorption behavior of sodium dodecyl sulfate was studied in detail by Batina et al. [119]. 

Alcohol sulfates commonly have free alcohol and electrolytes as impurities. Other hydrophobic impurities can also be present. A method suitable for the purification of surfactants has been proposed by Rosen [120]. Consequently, commercial products have CMCs that deviate from the accepted reference values. This was demonstrated by Vijayendran [121] who studied several commercial sodium lauryl sulfates of high purity. The CMC was determined both by the conductimetric method and by the surface tension method. The values found were similar for both methods but while three samples gave CMC values of 7.9, 7.8, and 7.4 mM, close to the standard range of 8.0-8.2 mM, three other samples gave values of 4.1, 3.1, and 1.7 mM. The sample with a CMC of 7.9 mM was found to have a CMC of 8.0 mM with no detectable surface tension minima after purification and recrystallization. This procedure failed in all other cases. 

Figures 12 and 13 show plots of the surface tension of sodium dodecyl ether (1 EO) sulfate and sodium dodecyl sulfate (2 EO) sulfate vs. their bulk concentration in distilled water and in sodium chloride solutions of 0.1 and 0.5 M total ionic strength at 10, 25, and 40°C [125].

Table 17 shows the CMCs of sodium alcohol propoxysulfates at 20°C determined from surface tension measurements by the maximum bubble pressure [127] and Table 18 shows the critical micelle concentrations of sodium pro-poxylated octylphenol and propoxylated nonylphenol sulfates. Surface tension... 

FIG. 10 Surface tension vs. surfactant concentration for sodium dodecyl sulfate and sodium dodecyl ether (m EO) sulfates at 25 °C [124],... 

FIG. 11 Surface tension vs. log surfactant concentration for (O) sodium decyl ether (2 EO) sulfate, (A) sodium dodecyl sulfate, (A) sodium dodecyl ether (1 EO) sulfate, ( ) sodium dodecyl ether (2 EO) sulfate, and ( ) sodium tetradecyl ether (2 EO) sulfate at 25 °C [94]. 

Table 19 shows the efficiencies and effectiveness of several alcohol and alcohol ether sulfates and Tables 20 and 21 give some values of surface tensions. 

TABLE 21 Surface Tensions of Alcohol Ether Sulfates... 

The CMC of commercial AOS and other surfactants at 40°C has been determined by Gafa and Lattanzi [6] who plotted the surface tension of aqueous surfactant solutions against concentration. The surface tensions were determined with the ring method according to du Nouy. Table 5 gives their CMC values in mmol/L and the surface tension at the CMC in mN/m. Table 5 also contains CMC values of isomerically pure sodium alkyl sulfates, sodium alkylbenzene-sulfonates, sodium hydroxyalkanesulfonate, and sodium alkenesulfonates at 40°C, taken from the literature [39 and references cited therein]. 

Table 5 also shows that the CMC values of the three sulfated alcohol (AS) samples are in line with those of the isomerically pure sulfates. The surface tension values at the CMC of the AS samples are less than those observed with the other commercial samples, including the AOS compounds. 

Surfactants like sodium dodecyl sulfate reduce the surface tension at the liquid-gas interface considerably. In fact, the addition of surfactants in small... 

Recently, the newly developed time-resolved quasielastic laser scattering (QELS) has been applied to follow the changes in the surface tension of the nonpolarized water nitrobenzene interface upon the injection of cetyltrimethylammonium bromide [34] and sodium dodecyl sulfate [35] around or beyond their critical micelle concentrations. As a matter of fact, the method is based on the determination of the frequency of the thermally excited capillary waves at liquid-liquid interfaces. Since the capillary wave frequency is a function of the surface tension, and the change in the surface tension reflects the ion surface concentration, the QELS method allows us to observe the dynamic changes of the ITIES, such as the formation of monolayers of various surfactants [34]. 

The few examples of deliberate investigation of dynamic processes as reflected by compression/expansion hysteresis have involved monolayers of fatty acids (Munden and Swarbrick, 1973 Munden et al., 1969), lecithins (Bienkowski and Skolnick, 1974 Cook and Webb, 1966), polymer films (Townsend and Buck, 1988) and monolayers of fatty acids and their sodium sulfate salts on aqueous subphases of alkanolamines (Rosano et al., 1971). A few of these studies determined the amount of hysteresis as a function of the rate of compression and expansion. However, no quantitative analysis of the results was attempted. Historically, dynamic surface tension has been used to study the dynamic response of lung phosphatidylcholine surfactant monolayers to a sinusoidal compression/expansion rate in order to mimic the mechanical contraction and expansion of the lungs. 

Sodium 12-b u toxydodecyl sulfate surface tension, 8 2441 Sodium 2-acrylamido-2-methylpropane-sulfonate (AMPS), 20 487 Sodium 3-acrylamido-3-methylbutanoate (AMBA), 20 487... 

In the case of alkyl ether sulfates, an increase in the number of oxyethylene groups produces an opposite result (19 - 22). Fig. 3 shows a decrease of the critical miceTTe concentration (Cj ) and the concentration for a given surface tension (for example,... 

Fig. 5, curve 1, shows - for dodecyl ether sulfates - the areas occupied by a molecule at c as a function of the number, m,of EO groups. The values were calculated by the Gibbs equation from the surface tension measurements. For 0 - m - 2 there is an area increase with increasing m, however, considerably... 

In Fig. 7, this is exemplified with surface tension concentration curves for Na n-tetradecyl diethyleneglycol ether sulfates (33). Less soluble surfactants would produce with increasing water hardness increased formation of sparingly soluble Ca salts. Therefore, the critical micelle concentration would be shifted toward much larger concentrations. 

However, in the case of Na tetradecyl dioxy-ethylene sulfate, the surface tension and the critical micelle concentration will be reduced in the presence of water hardness. If a complexing agent is added, the effect is weakened because of the complexing of the... 

In this modification, the ionic micelle has been considered as the charged phase, which has difficulties from the thermodynamic viewpoint. The precise measurement of the surface tension of aqueous sodium dodecyl sulfate solutions revealed the cotlnuous decrease of surface tension above the cmc and indicated that the charged phase separation model is not correct (27). ... 

The application of the activity of the surfactant has been examined also for the surface tension and adsorption of disodlum alkyl phosphate(6,7), sodium dodecyl sulfate(37), alkyl trimethylammonium bromide(35 ), and sodium perfluorooctanoate(13) solutions. These studies show that the surface tension and theadsorption amount are controlled by the activity of surfactant, irrespective of the added electrolyte concentration. 

Table 3 Results of the regression analysis for adsorption and surface tension of sodium alkyl sulfate homologues ...

The adsorption of ionic surfactants creates an adsorption layer of surfactant ions, a Stern layer of counterions and a diffusive layer distributed by the electric field of the charged surface. Every layer has its own contribution to surface tension. For example, the adsorption of dodecyl sulfate (DS") ions from the sodium dodecyl sulfate solution is described by the modified Frumkin isotherm as... 

Equation 56 presents an improvement of Eq. 40 for predicting surface tension of ionic surfactants. For adsorption of alkali dodecyl sulfates, experimental data are available for the adsorption at saturation Ao and for the equihbrium constant Ki [55]. Table 6 summarizes the available data for alkali dodecyl sulfates. fSi, and A are calculated using Eqs. 52-54. The value for the di-... 

Table 6 Experimental data, calculated data, and best-fitted results for su obtained for the adsorption and surface tension of alkali dodecyl sulfates ...

---