1-Pentanol, solubilization

The behaviors of POE and pentanol as far as changes of I1/I3 and n are concerned can be explained as follows. A pentanol molecule is solubilized in a micelle with its hydroxyl group anchored at the micelle surface, and its alkyl chain going through the palisade layer and reaching the micelle hydrophobic core. The solubilized pentanol thus affects the palisade layer, where pyrene is solubilized, over its whole thickness. Upon pentanol solubilization some of the water present in the palisade is released, resulting in a decrease of its overall polarity, which is sensed by pyrene. On the contrary, the POE repeat units interacting with the micelles remain located near the micelle outer surface. Thus, if the only effect of the POE-micelle interaction were a release of some of the... 

At infinite dilution, 1-pentanol monomers distribute between AOT-reversed micelles and the continuous organic phase, whereas at finite alcohol concentration, given the ability of alcohol to self-assemble in the apolar organic solvent, a coexistence between reversed micelles (solubilizing 1-pentanol) and alcoholic aggregates (incorporating AOT molecules) is realized [25],... 

In contrast to the above results, all three "picket fence" porphyrins are solubilized in an oil-in-water microemulsion to yield a clear solution having a Soret band at 419-421 nm resembling that of H2PF,TPro solubilized in micelles. In this case the microemulsion (composed of SDS, n-pentanol and dodecane) consists of oil "droplets" dissolved in bulk water the radius of the droplet has been estimated to be 37 A ( ), well over twice that estimated for an SDS micelle (16 A). Since the droplet in the microemulsion contains a much larger "interior", it is reasonable that it may be a better medium for solubilizing the porphyrin. 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

Many reports are available where the cationic surfactant CTAB has been used to prepare gold nanoparticles [127-129]. Giustini et al. [130] have characterized the quaternary w/o micro emulsion of CTAB/n-pentanol/ n-hexane/water. Some salient features of CTAB/co-surfactant/alkane/water system are (1) formation of nearly spherical droplets in the L2 region (a liquid isotropic phase formed by disconnected aqueous domains dispersed in a continuous organic bulk) stabilized by a surfactant/co-surfactant interfacial film. (2) With an increase in water content, L2 is followed up to the water solubilization failure, without any transition to bicontinuous structure, and (3) at low Wo, the droplet radius is smaller than R° (spontaneous radius of curvature of the interfacial film) but when the droplet radius tends to become larger than R° (i.e., increasing Wo), the microemulsion phase separates into a Winsor II system. 

So far it has not been possible to measure the chemical potentials of the components in the mesophases. This measurement is possible, however, in solutions which are in equilibrium with the mesophases. If pure water is taken as the standard state, the activity of water in equilibrium with the D and E phases in the system NaC8-decanol-water is more than 0.8 (4). From these activities in micellar solutions, the activity of the fatty acid salt has sometimes been calculated. The salt is incorrectly treated as a completely dissociated electrolyte. The activity of the fatty acid in solutions of short chain carboxylates has also been determined by gas chromatography from these determinations the carboxylate anion activity can be determined (18). Low CMC values for the carboxylate are obtained (15). The same method has shown that the activity of solubilized pentanol in octanoate solutions is still very low when the solution is in equilibrium with phase D (Figure 10) (15). 

Figure 10. The activity of n-pentanol in micellar solutions of sodium octanoate with solubilized pentanol and in equilibrium with the lamellar mesophase D. The abscissa indicates the mole fraction of sodium octanoate in the system (15).

In this paper, a molecular thermodynamic approach is developed to predict the structural and compositional characteristics of microemulsions. The theory can be applied not only to oil-in-water and water-in-cil droplet-type microemulsions but also to bicontinuous microemulsions. This treatment constitutes an extension of our earlier approaches to micelles, mixed micelles, and solubilization but also takes into account the self-association of alcohol in the oil phase and the excluded-volume interactions among the droplets. Illustrative results are presented for an anionic surfactant (SDS) pentanol cyclohexane water NaCl system. Microstructur al features including the droplet radius, the thickness of the surfactant layer at the interface, the number of molecules of various species in a droplet, the size and composition dispersions of the droplets, and the distribution of the surfactant, oil, alcohol, and water molecules in the various microdomains are calculated. Further, the model allows the identification of the transition from a two-phase droplet-type microemulsion system to a three-phase microemulsion system involving a bicontinuous microemulsion. The persistence length of the bicontinuous microemulsion is also predicted by the model. Finally, the model permits the calculation of the interfacial tension between a microemulsion and the coexisting phase. 

Fig. 3. Schematic representation of the solubilization of nonane (upper left), n-pentanol (lower left) and a small ionic species (right) by a spherical ionic micelle (Kavanau, 1965).

Fig. 2-13. Schematic two-dimensional representation of the solubilization of (b) n-nonane as a nonpolar substrate, and (c) 1-pentanol as another amphiphile, by a spherical ionic micelle (a) of an -decanoic acid salt in water.

The solubilization of an aqueous sodium chloride solution by potassium oleate in the pentanol isotropic solution was determined. The presence of sodium chloride increased the minimum concentration for solubilization, reduced the maximum solubilization at high pentanohpotassium oleate ratios, and altered this ratio to lower values for maximal solubilization of the electrolyte solution. The increased minimum amount of electrolyte solution for solubilization arose from the fact that no micelles were present at the lowest fractions of water in the pentanol solution. The increased potassium oleate. pentanol ratio for maximal solubilization of the electrolyte was related to the destabilization of the lamellar liquid crystal with which the inverse micellar pentanol solution of high water content was in equilibrium. 

These inverse micelles will solubilize electrolytes in their aqueous core but the presence of the electrolytes also will influence the stability of the inverse micelle. A change in the stability of the inverse micelle will be reflected in modifications of the solubility region of the inverse micellar solution. This chapter will relate the changes in solubility areas from addition of electrolytes to the water to the structure of inverse micelles and other association complexes in the pentanol solution. 

The change of solubility areas with electrolyte content is shown in Figure 2. The solubility area for the pentanol solution of potassium oleate and water (—. —. —, Figure 2) shows a minimum water amount for solubilization. The minimum amount of water is proportional to the amount of soap present the solubility limit to the right gives a molecular water potassium oleate ratio of three, the minimum number of water molecules to bring the soap into solution. The solubility area is approximately triangular with maximum water solubilization at 12% (w/w) potassium oleate, 33% pentanol, and 55% water. The potassium oleate pentanol ratio is. 36 at that point. 

In the presence of 15% pentanol, large amounts of water can be solubilized into heptane or toluene solutions of Ci2-Ci6 alkylpyridinium or alkyltrimethylammo-nium bromides (Venable, 1985). In heptane/pentanol, the longer-chain surfactants appear to be more effective than the shorter ones, while in toluene/pentanol the shorter ones appear to be more effective. In both solvent mixtures, the pyridinium salts are more effective solubilizers than the corresponding trimethylammonium salts. All the quaternaries investigated were more effective than sodium dodecyl sulfate. 

FIG. 10 Regulation of the catalytic activity of solubilized enz5unes by variation of the surfactant concentration at a constant degree of hydration in the systems ( ) AOT-water-octane (A) dodecylammonium propionate-water-riiethyl ether/benzene (O) Brij 96-water-cyclohexane ( ) lecithin-water/methanol/pentanol-octane. Dashed lines show levels of corresponding catalytic activities in aqueous solution. (From Ref. 10.)... 

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