Micellization azeotropes

As also seen in Table I, the micellar composition can be a-f-fected substantially by nonideality. In -fact, azeotropic behavior in the monomer—micelle equilibrium is possible -for these nonideal systems i.e., as the monomer composition varies -from pure A to pure B, the micelle can vary -from Xn > y to Xn = y (azeotrope) to Xa < yA. This azeotrope -formation is illustrated -for the cationic/nonionic system in Figure 2, where an azeotrope -forms at Xa = yA = 0.3. The minimum CMC -for a mixture corresponds to the azeotropic composition i-f an azeotrope is present (32.37). For an ideal system, azeotropic behavior is not observed. 

The mass action model (MAM) for binary ionic or nonionic surfactants and the pseudo-phase separation model (PSM) which were developed earlier (I EC Fundamentals 1983, 22, 230 J. Phys. Chem. 1984, 88, 1642) have been extended. The new models include a micelle aggregation number and counterion binding parameter which depend on the mixed micelle composition. Thus, the models can describe mixtures of ionic/nonionic surfactants more realistically. These models generally predict no azeotropic micellization. For the PSM, calculated mixed erne s and especially monomer concentrations can differ significantly from those of the previous models. The results are used to estimate the Redlich-Kister parameters of monomer mixing in the mixed micelles from data on mixed erne s of Lange and Beck (1973), Funasaki and Hada (1979), and others. 

Azeotrope Micellization. Here the micelle mole fraction of 1 is the same as that of the monomers (10.111. For fixed a = the monomer and micelle compositions are equal to a for all total surfactant concentrations. If an azeotrope exists, this azeotropic condition and Equation 5 imply that... 

Azeotrope Micellization. Again, if azeotrope exists, x = a = a. Then for all total surfactant concentrations above the cmc this condition and Equations 15 and 16 imply that... 

This equation contains the counterion concentration Cj + which depends on the total surfactant concentration. It follows that x would depend on c j+ and hence would vary above the cmc. This contradiction implies that azeotrope micellization cannot occur if = J3(x). Of course, if c c, the C + would be constant and azeotropy can again occur. If d fdx = 0, azeotropy can be also possible. For ySj = / 2 = 0.7, Cj = 0, c /cj = 3.0, and w(x) = A + B ( 2x-l), which is the Redlich-Kbter expansion (12), with A = -3 and B = 0, one finds from Equation 21 that 0.8113. No value of Qj can be calculated if = 0.7, / 2 = 0.3, and / (x) = iX + /32(1 x). Figures 1 and 2 illustrate this point showing monomer and micelle concentrations (or inventories) for a = 0.8113. In the ionic/ionic case, the micelle composition x and the ratio Cj/c2 are constant above the cmc. In the ionic/nonionic case (Figure 2) the micelle composition varies with total surfactant concentration. Osborne-Lee and Schechter (22) have found evidence of azeotrope micellization for... 

Figure 1. Inventories and micelle compositions for azeotrope micell-ization of mixed ionic surfactants, c /cj = 3.0, A = - 3.0, B = 0.0, j3i = 2 0-7 AZ 0.8113.

For 13 = P(x) and N=N(x), the MAM predicts no azeotrope micellization. For P = P ), the PSM predicts no azeotrope micellization unless the salt concentration is substantially higher than the surfactant concentration. 

Sodium di(ethylhexyl)sulfosuccinate (Aerosol-OT, sodium docusate) [577-11-7] M 444.6. Dissolve it in MeOH and the inorganic salts which precipitate are filtered off. Water is added and the solution is extracted several times with hexane. The residue is evaporated to one-fifth its original volume, benzene is added and azeotropic distillation is continued until no water remains. The solvent is evaporated. The white residual soHd is crushed and dried in vacuo over P2O5 for 48hours [El Seoud Fendler J Chem Soc, Fcrcukiy Trans 1 71 452 1975]. [Beilstein 4 IV 114.] It solubilises major myelin trans membrane proteolipids, and forms reverse micelles in hydrocarbon solvents. 

Jette, K.K. et al, 2004. Preparation and drug loading of poly(ethylene g yco )-block-poly(epsilon-caprolactone) micelles through the evaporation of a cosolvent azeotrope. Pharmaceutical Research, 21(7), 1184-1191. 

Ashakawa et al. (1997) report CMC data as shown in the figure for mixtures of a partially fluorinated lithium decyl sulfate (1) and hthium tetradecyl sulfate (2). Analyze assuming ideal solution theory in the bulk solution and regular solution theory in the micelles. Show that an azeotrope is formed in this system. Plot x, as a funetion of Xj/(x, +... 

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