Four-component surfactant system

Microemulsions are thermodynamically stable mixtures. The interfacial tension is almost zero. The size of drops is very small, and this makes the microemulsions look clear. It has been suggested that microemulsion may consists of bicontinuous structures, which sounds more plausible in these four-component microemulsion systems. It has also been suggested that microemulsion may be compared to swollen micelles (i.e., if one solubilizes oil in micelles). In such isotropic mixtures, short-range order exists between droplets. As found from extensive experiments, not all mixtures of water-oil-surfactant-cosurfactant produce a microemulsion. This has led to studies that have attempted to predict the molecular relationship. 

In 1959, J. H. Schulman introduced the term microemulsion for transparent-solutions of a model four-component system [126]. Basically, microemulsions consist of water, an oily component, surfactant, and co-surfactant. A three phase diagram illustrating the area of existence of microemulsions is presented in Fig. 6 [24]. The phase equilibria, structures, applications, and chemical reactions of microemulsion have been reviewed by Sjoblom et al. [127]. In contrast to macroemulsions, microemulsions are optically transparent, isotropic, and thermodynamically stable [128, 129]. Microemulsions have been subject of various... 

Candau, F. Ballet, F. "Formation and Structure of Four -Component Systems Containing Polymeric Surfactants" in "Microemulsions Robb I. D. Plenum Press New York, 1982 p. 59. 

Ceglie, A., Das, K. P, and Lindman, B. (1987), Microemulsion structure in four component systems for different surfactants, Coll. Surf, 28,29 40. 

Mlcroemulslons are related to micellesThe most common, the four component mlcroemulslons, are constructed from a hydrocarbon, a surfactant, a short chain alcohol (cosurfactant) and water. When the hydrocarbon component present is significantly larger than the water component the mlcroemulslon Is generally a water-ln-oll (w/o) mlcroemulslon. Figure Id. This designation arises by virtue of the fact that the water is present In the form of spheres. Invisible to the naked eye (250 to lOOoR In diameter), dispersed throughout the hydrocarbon continuum. The surfactant and cosurfactant stabilize these water-rich droplets and help render them thermodynamically stable. These systems are optically transparent and can contain up to 0.3Xn ... 

On the other hand, microemulsion system could combine hydrothermal methodology to enhance the crystallization of NPs. Yan et al. s)mthe-sized t-YVOi NPs by CTAB microemulsion assisted hydrothermal reaction (Sun et al., 2002). As a t)q)ical four-component reverse micelle system, the solution contained surfactant CTAB, cosurfactant n-hexanol, oil phase n-heptane and water phase with inorganic salt. When the W value (the molar ratio of water/CTAB) was below 16, the sizes of NPs could be mediated in the range of 9-50 nm by adjusting the... 

Ternary Surfactant System. The results for the three-component surfactant mixtures are summarised in figure 11. Clearly there are four main regions ... 

In the simplest possible case, the systems reported on below contain only four components—the alkane, water, sodium chloride and a monoisomeric surfactant. Alcohol cosurfactants were not usually employed, but their presence does not appear to influence the results significantly (14). 

Consequently, the following four components were selected to prepare the photoresponsive emulsion system equal volumes of n-dodecane and 0.3 M NaNOs aqueous solution, the C12E4 surfactant, and an azobenzene-modified poly(acrylate). C12E4 is known to stabilize direct and inverse emulsions below and above the so-called phase inversion temperature (PIT here 24°C), respectively. Emulsions are unstable in the vicinity of the PIT, a temperature domain corresponding to the CTR of the light-responsive system. Emulsions made of equal oil and water volumes are directly below the PIT (and display a high electric conductivity because of the water continuum), but inverse (and of low conductivity) above the PIT (Khoukh et al., 2005). 

Although liquid crystal (LC) theory predicts the existence of as many as 18 distinct structures for a given molecular composition and structure. Nature appears to have been kind in that only four of those possibilities have been identified in simple, two-component surfactant-water systems. The four LC phases usually associated with surfactants include the lamellar, hexagonal (normal and inverted), and cubic (Fig. 15.3). Of the four, the cubic phase is the most difficult to define and detect. It may have a wide variety of structural variations including a bicontinuous or interpenetrating structure that involve components of the other mesophases. The remaining types are more easily characterized and, as a result, better understood. 

From the above, it seems clear that the effects of an added nonelectrolyte on the solubilizing capacity of a given surfactant system may be quite complex and may not lend itself to easy analysis. It can be assumed, however, that the fundamental relationships that exist between the solutes and the micellization characteristics of the surfactant, in the absence of the solubihzed additive, can be used to good advantage in predicting what may reasonably be expected in the four-component system. 

Most microemulsions are made with four components. In this case, Eq. 2.20 cannot be used, unless a pseudo-component is defined, such as a given ratio of surfactant to alcoholic cosurfactant. This active mixture is considered as the third component and is placed at the C apex. Figure 2.16 shows the phase diagram of the ternary system water/heptane/sodium bis (2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) [35]. AOT is an anionic surfactant able to form W/0 microemulsions without the need of a cosurfactant. Figure 2.17 shows the phase diagram of the pseudo-ternary system water/heptane/(CTAB + w-butanol) [31]. CTAB is a cationic surfactant that needs to be associated with a cosur ctant to form microemulsions. The ratio CTAB/butanol was constant (1/1 w/w) for all compositions represented in the phase diagram. The hatched areas corres-... 

Microemulsions consist of either three or four components two solvents, a surfactant, and sometimes an alcohol/cosurfactant. This complexity of composition means that there are potentially many relaxation processes. Despite this, microemulsion kinetics has been relatively well researched due to sustained interest in their structure and optimization. There have been several important reviews of the area, including summaries of work on the dynamic processes in such systems [100,101]. 

The oil-in-water (o/w) type of creams (Fig. 1) are systems of four components their main elements are the hydrophilic and lipophilic gel phases. Both phases are composed of bilayers of mixed crystals. Water molecules are enclosed between the surfactant and alcoholic groups of the emulsifier molecules. In the gel phase, water molecules in interlamellar binding are in equilibrium with water molecules bound as bulk water. Both aqueous phases constitute the coherent (outer) phase of the system. The surplus of cetostearyl alcohol, which is not part of the hydrophilic gel phase, forms a matrix of lipophilic character called the lipophilic gel phase. The disperse or inner phase is mechanically not removable from the lipophilic gel phase. The lipophilic gel phase is constituted exclusively by cetostearyl alcohol, which can form only a semihydrate water layer [1,2]. 

As already mentioned in the Introduction, micelles and microemulsions are complex multicomponent fluids consisting of two liquids, namely water and oil, and a surface-active agent (for a three-component system). For a four-component system, in addition to the surfactant a cosurfactant is also added (usually an alcohol). In systems containing more than four components, some salt is added, solubilized in either water or oil. 

As far as the water phase is concerned, it must be pointed out that the measured A// value never equals the expected AHl value corresponding to the sample s known water content. Part of the water is, in fact, bound to the hydrophilic groups of the surfactant and, for example in the case of our four-component system, part of the water is also involved in the thermal events occurring in the low-temperature part of the DSC spectrum (see Fig. 15, curve 5). In the case of our three-component systems, the information about the amount of water not behaving as free, but linked with the system s interphase region, is obviously more immediate. 

FIG. 15 Water-hexadecane system (Table 2). DSC-ENDO spectra of the upper isotropic phase of biphasic samples with increasing water concentration of the sample as a whole. Curve 1 Ctoi = 0.372, the first appearance of a birefiingent liquid crystalline lens. Curve 2 Ct = 0.388. Curve 3 Ct = 0.419. Curve 4 Melting endotherms of the Uquid crystalline bottom mesophase of a sample with Ct , = 0.419. AH and AHb are the thermal contributions of the n-hexanol and the water-K-oleate-hexanol mixture, respectively. (From Ref. 23.) Curve 5 DSC-ENDO spectrum of the ternary mixture n-hexanol-K-oleate-water. The proportions between surfactant and cosurfactant are the same as those used to formulate the four-component W/O microemulsions. 

FIGURE 1.59 Four component system oil (O)-water (W)-emulsifier (E)-co-surfactant (S) (ratio of 0 S versus S W). 

The interfacial tension can undergo significant changes if the polarity of the medium is altered, such as in the stability/coagulation transition caused by the addition of water to hydrophobic silica dispersions in propanol or ethanol [44,52,53]. Also, the addition of small additives of various surface-active substances can have a dramatic effect on the structure and properties of disperse systems and the conditions of transitions [14,16,17,26]. The formation and structure of stable micellar systems and various surfactant association colloids, such as microemulsion systems and liquid crystalline phases formed in various multicomponent water/hydrocarbon/surfactant/alcohol systems with varying compositions and temperatures, have been described in numerous publications [14-22,78,79,84-88]. These studies provide a detailed analysis of the phase equilibria under various conditions and cover all kinds of systems with all levels of disperse phase concentration. Special attention is devoted to the role of low and ultralow values of the surface energy at the interfaces. The author s first observations of areas of stable microheterogeneity in two-, three-, and four-component systems were documented in [66-68],... 

Abstract We have studied the equilibrium between a lamellar phase and crystalline salts in a four-component system containing both a cationic and an anionic surfactant in water. The chemical potentials for the different components have been derived from a thermodynamic model for the free energy. 

In a series of papers we have developed a model for the thermodynamic properties of ionic surfactant-water systems [3-5]. This has led to fairly satisfactory description of phase equilibria in two and three component systems. As a continuation of this work we present a study of a model four-component system HiO-A X - A X where A and A are an anionic and a cationic surfactant, respectively, while X""X forms an ordinary electrolyte. Dealing with four components in studies of phase equilibria poses a substantial problem due to the complexity... 

The problems of applying the previously developed thermodynamic model to a four-component system has been investigated. It is shown that at least for the restricted applications to equilibria between a lamellar phase and crystals the computational problems can be solved using only a minicomputor. We further expect that the calculations will be of considerable help in the experimental studies of anionic surfactant-cationic surfactant-water systems that are currently performed in this laboratory. 

While studying phase formation when surfactants - hydrocarbon oil mixtures (i.e. three component systems) were added to increasing amounts of water (i.e. forming four component systems) it was observed that those systems which initially developed large quantities of liquid crystalline phases later formed better, finer emulsions than those systems that initially consisted of isotropic phases. These observations and their association with the process of self emulsification or easy emulsion formation in the systems investigated are presented in this report. 

Four-component systems were prepared by dissolving the surfactants in the hydrocarbons and adding the appropriate amount of water (all preparations by weight %). 

The typical phases observed in the four component systems are illustrated in figures 7 and 8. It is seen that those systems containing 10 per cent water formed large areas of isotropic organic liquid phase (L2). This phase consisted of water solubilized within the cores of the inverted micelles of the surfactants in the... 

First, it is obvious that none of the Winsor diagrams will match this behavior because the amphiphile mixture has a varying affinity that depends on the relative amounts of, for instance, a hydrophilic surfactant (S) and a lipophilic alcohol (A). A quaternary diagram is required to handle this four-component system (e.g., a regular tetreihedron with equal sides). At each vertex, one of the components is represented. 

A similar three-liquid region was observed by Ali and Mulley [28] in a quaternary system containing dodecane, water and two non-ionic surfactants, CjoE and C10E3. The compositions involved were near the face of the tetrahedron representing the four-component system and containing about equal quantities of water and dodecane and 1 to 2.5 % C qE, Addition of 3 to 7.2 % C10E3 to this two-phase, three-component system in the face of the tetrahedron, produced the system with three liquid phases in equilibrium. The lower liquid... 

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