Microemulsion four component

S. Ezrahi, E. Wachtel, A. Aserin, N. Garti. Structural polymorphism in a four component nonionic microemulsion. J Coll Interface Sci 797 277-290, 1997. 

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... 

The extent to which the vehicle can affect the entire diffusion process can be shown by an example. In a four-component system of 40% oil, 40% water, and 20% of an emulsifying agent and coemulsifier, alteration of only the proportion of emulsifier to coemulsifier leads to systems of completely different colloidal-chemical structures, which can be labeled as either creams, gels, or microemulsions. 

Emulsifier will be found in both these phases. On the other hand, in systems with four components (Figure 9.4), consisting of oil-water-detergent-cosurfactant, there exists a region where a clear phase is found. This is the region where microemulsions are found. 

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. 

Terpene-based microemulsion cleaning composition has been reported in some industrial applications. Oil-in-water microemulsion cleaning compositions comprising four principal components were described based on four components. These were... 

Agostiano A, Catalano M, Curri ML, Della Monica M, Manna L, Vasanelli L (2000) Synthesis and structural characterisation of CdS nanoparticles prepared in a four-components water-in-oil microemulsion. Micron 31 253-258... 

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. 

A totally different way of looking at microemulsions —and one that connects this topic with previous sections of the chapter —is to view them as complicated examples of micellar solubilization. From this perspective, there is no problem with spontaneous formation or stability with respect to separation. Furthermore, ordinary and reverse micelles provide the basis for both O/W and W/O microemulsions. From the micellar point of view, it is the phase diagram for the four-component system rather than y that holds the key to understanding microemulsions. 

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

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... 

This chapter describes the liquid phases in some four-component systems, a treatment that demonstrates the identity between colloidal solutions and microemulsions and gives information about the important factors for their stability. 

In general it is very difficult to pin down the microstructure of microemulsions. Scattering probes yield only a single, broad scattering maximum, which taken cdone is not very informative. To further aggravate the problem, many microemulsions consist of at least four components. Since the usual co-surfactant additive can partition between oil and water and the interface between them, it is impossible to sort out the structural... 

Figure 6.1 Schematic diagram of a four-component w/o microemulsion droplet.

It is interesting to note that this Scandinavian contribution was in agreement with Schulman s original concept of microemulsions as micellar solutions [3] the name microemulsions was coined much later [27]. Following Gillberg et al.. Ranee and Friberg [28] demonstrated that the O/W microemulsion is a direct continuation of the well-known Ekwall et al. aqueous micellar solutions [17] (Fig. 3). It should be noted that the common presentation of these four-component phase diagrams as phase maps in one plane... 

Figure 11 Relative self-diffusion coefficients of ( ) water and (A) oil as a function of the oil content in a four-component microemulsion, AOT-water-NaCl-isooctane.The system is tuned by temperature at constant salinity. (Data taken from Ref. 45.)...

Figure 4 Cartoon of the interfacia region of a four-component microemulsion composed of an ionic surfactant and its counterion, an alcohol, water, and oil. The amphiphilic arenediazonium ion probe, 16-ArN, is shown with its reactive headgroup located in the interfacial region.

In the case of thermal initiation of styrene [79,80], the polymerization rate was found to be proportional to [AIBN] and [KPS] , in good agreement with other data for three- or four-component microemulsions [66,81]. The dependence on AIBN concentration is consistent with the prediction of 0.40 based on the micellar nucleation theory in emulsion polymerization (Smith-Ewart case 2) (see, e.g.. Ref 129). The dependence on KPS concentration lies between this case and the value of 0.5 for solution or bulk polymerization. 

A microemulsion is water/hydrocarbon dispersion stabilized by an ionic surfactant such as a soap, alkyl sulphate or sul-phonate and most often also contains a cosurfactant in the form of a medium chain length alcohol (pentanol). Of these four components water, surfactant and cosurfactant are called the structure forming elements since they form colloidal association structures similar to the microemulsions with no hydrocarbon present. The formulation and preparation of microemulsions is greatly enhanced by a knowledge of these composition dependent structures, hence an introductory description of them will be given. 

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-... 

Figure 9 Envelopes of [he various zones obtained in a simulation of a microemulsion, which consists of a mixture of four components. (Reprinted from Ref. 42. with permission of Elsevier Scicnce-NL. The Netherlands. ...

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]. 

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. 

FIG. 10 (a) Melting endothenns of four-component W/O microemulsions (Table 2). 

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. 

The evolution of the DSC-EXO spectra for a three-component water-isooctane microemulsion (Table 3) as a function of the water concentration is reported in Fig. 23, where, for the sake of comparison, the DSC-ENDO spectra are also shown. The same analysis is reported for four-component microemulsions in Fig. 24. In the case of the water-dodecane system, as shown in Fig. 24a for a sample with a high water concentration (C = 0.252), the freezing of the oil = 258 K) does not prevent the free water fraction of the sample from freezing at the lower temperature of =248 K. (See also Fig. 21 for a sample of the same system with C = 0.150.)... 

Fannn, M., Wachtel, E., Antalek, B., Aserin, A., and Garti, N. 2001 A study of the microstructure of four-component sucrose ester microemulsions hy SAXS and NMR, Colloids Surf., A 180 173-186. 

Billman, J.F. and Kaler, E.W. 1991 Structure and phase behavior in four-component nonionic microemulsions, Langmuir 7 1609-1617. 

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