Surfactant decanol

FIG. 7 Phase diagram (incomplete) for the three-component system water-dehydroabietic acid surfactant-1-decanol at 25 °C. The one-phase areas are LC lamellar liquid crystalline phase and L isotropic solution (a) DeHAb-EOll, (b) DeHAb-E022. (Reproduced from Ref. 59.)... 

An example for a partially known ternary phase diagram is the sodium octane 1 -sulfonate/ 1-decanol/water system [61]. Figure 34 shows the isotropic areas L, and L2 for the water-rich surfactant phase with solubilized alcohol and for the solvent-rich surfactant phase with solubilized water, respectively. Furthermore, the lamellar neat phase D and the anisotropic hexagonal middle phase E are indicated (for systematics, cf. Ref. 62). For the quaternary sodium octane 1-sulfonate (A)/l-butanol (B)/n-tetradecane (0)/water (W) system, the tricritical point which characterizes the transition of three coexisting phases into one liquid phase is at 40.1°C A, 0.042 (mass parts) B, 0.958 (A + B = 56 wt %) O, 0.54 W, 0.46 [63]. For both the binary phase equilibrium dodecane... 

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]. 

On the other hand, with microemulsions based on an anionic surfactant and a long chain alcohol, was fairly low for certain concentrations, indicating that distinct water droplets in a hydrophobic medium may form. The system investigated by Lindman et al (29-34) was based on octanoic acid - decanol -octane-water. This means that the anionic "surfactant" used contains only seven carbon atoms in the alkyl chain which is fairly short. With longer chain surfactants, one would expect well defined "water cores" provided the alcohol is also long-chain. Such well defined "water cores" have also been confirmed by Lindman et a (34) for the Aerosol OT - hydrocarbon system. 

As expected, the influence of added nonelectrolytes can be quite different depending on whether the added compound is likely to be located in the micelles or in the in-termicellar solution. The effect of normal alcohols has been studied in detail for potassium dodecanoate the CMC is lowered for all alcohols studied but the effect increases considerably in going from ethanol to decanol (cf. Fig. 2.7). Hydrocarbons, like cyclohexane, n-heptane, toluene, and benzene, have been found to lower the CMC for many surfactants. Strongly hydrophilic substances, like dioxane and urea, have small and complex effects. At higher concentrations they markedly increase the CMC or even inhibit micelle formation. Addition of another similar surface-active agent generally gives a CMC in between the CMCs of the two surfactants. 

The mixing behavior of 10-(perfluorohexyl)-decanol and DPPC in Langmuir monolayers has recently been reported, showing partial miscibility, especially at low surface pressure [67], 10-(perfluorohexyl)-Decanol was studied because it is a fluorinated analog of hexadecanol, which has been used in synthetic lung surfactant compositions. 

In the method developed by Exerowa, Cohen and Nikolova [144] the insoluble (or slightly soluble) monolayers are obtained by adsorption from the gas phase. A special device (Fig. 2.28) was constructed for the purpose a ring a in the measuring cell of Scheludko and Exerowa for formation of microscopic foam films at constant capillary pressure (see Section 2.1.2.). The insoluble (or slightly soluble) substance from reversoir b is placed in this ring. Conditions for the adsorption of the surfactant on either surface of the bi-concave drop are created in the closed space of the measuring cell. The surfactant used was n-decanol which at temperatures lower than 10°C forms a condensed monolayer. Thus, it is possible to obtain common thin as well as black foam films. The results from these studies can be seen in Section 3.4.3.3. 

Finally in this section, Swager [200] reported amphiphilic complexes of oxova-nadium(IV) (Figure 108) which he studied in both binary (surfectant plus water) and ternary (surfactant plus water plus decanol) systems, finding both lamellar (L ) and hexagonal (Hi) phases. 

The solubility of n-decanol in the LI phase is also important (up to 12% at the end of the LI phase). The LI phase is accountable for the observation of oil-inwater (o/w) microemulsions. The La domain, generally located in the middle of the diagram, points toward the water side for a critical surfactant-to-cosurfactant ratio. (A 1 2 sodium octanoate to n-decanol ratio leads to a lamellar phase with as little as 17% surfactant-cosurfactant mixture.) In some cases, such as for octyl trimethylammonium bromide (OTAB)-hexanol-water, the lamellar phase already exists for 3% hexanol + 3% OTAB ... 

To obtain a wide w/o microemulsion phase it is essential to adjust carefully the cosurfactant structure (usually its chain length) and its relative amount. Although trial and error is still the most commonly used method for obtaining microemulsions, a tentative rule is to combine a very hydrophobic cosurfactant (n-decanol) with a very hydrophilic ionic surfactant (alcohol sulfate) and a less hydrophobic cosurfactant (hexanol) with a less hydrophilic ionic surfactant (OTAB). For very hydrophobic ionic surfactants, such as dialkyl dimethylammonium chloride, a water-soluble cosurfactant, such as butanol or isopropanol, is adequate (this rule derives at least partially from the fact that an important feature of the cosurfactant consists of readjusting the surfactant packing at the solvent/oil interface). 

Polymeric quaternary ammonium surfactants made from w-dodecyl bromide and poly(2-vinylpyridine) are better solubilizers for oil-soluble azo dyes and for n-decanol than monomeric quaternary cationics with similar (monomeric) structures (Tokiwa, 1963 Inoue, 1964). Solubilization of n-decanol in the polycationics increased as the alkyl chain content increased to a maximum at 24% alkyl content and resulted, at high decanol content, in intermolecular aggregation of the poly cationic molecules (Inoue, 1964). 

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