Mesophases mixed surfactant systems

Chapter 1 presents an overview of fluorinated surfactants. The synthesis of fluorinated surfactants is discussed in Chapter 2. Since the space limitations precluded a detailed description of processes, patent citations are augmented by references to Chemical Abstracts. Physical and chemical properties are reviewed in Chapter 3. Chapters 4-7 are devoted to the theory of fluorinated surfactants liquid-vapor and liquid-liquid interface (Chapter 4), solid-liquid interface (Chapter 5), solutions of fluorinated surfactants (Chapter 6), and the structure of micelles and mesophases, including mixed surfactant systems, in Chapter 7. The practical application of fluorinated surfactants is the subject of Chapter 8. Various applications are listed in alphabetical order for easy access to information. Chapter 9 reviews the analytical and physical methods for the investigation of fluorinated surfactants. Chapter 10 examines the environmental and toxicological aspects, including the use of fluorinated surfactants in biological systems. 

Obviously, the presence of mesophases or other structures such as, for example, mixed surfactant complexes, can not only increase the stability of the foam from a surface chemical standpoint but can also significantly enhance the physical strength of the system. When thinning reaches the point at which bubble rupture becomes important, the mechanical strength and rigidity of such structures might help the system withstand the thermal and mechanical agitation that would otherwise result in film failure and foam collapse. 

Recently reported meso- and macroscale self-assembly approaches conducted, respectively, in the presence of surfactant mesophases [134-136] and colloidal sphere arrays [137] are highly promising for the molecular engineering of novel catalytic mixed metal oxides. These novel methods offer the possibility to control surface and bulk chemistry (e.g. the V oxidation state and P/V ratios), wall nature (i.e. amorphous or nanocrystalline), morphology, pore structures and surface areas of mixed metal oxides. Furthermore, these novel catalysts represent well-defined model systems that are expected to lead to new insights into the nature of the active and selective surface sites and the mechanism of n-butane oxidation. In this section, we describe several promising synthesis approaches to VPO catalysts, such as the self-assembly of mesostructured VPO phases, the synthesis of macroporous VPO phases, intercalation and pillaring of layered VPO phases and other methods. 

In this section, we will focus on the solubilization of a substance in water-oil-surfactant samples containing initially three components. These ternary systems include microemulsions (w/o, o/w and bicontinous), lamellar phases and other liquid crystal mesophases. On a microscopic scale, oil microdomains are separated from water microdomains by a surfactant interface. A microdomain is here understood to be an aggregate of at least the order of a hundred self-assembled molecules, although being too small to be considered as a microphase-separated sample. A sample contains separated microphases when domains of micron size of two thermodynamically stable different phases co-exist and do not de-mix even after centrifugation, due to kinetic stability. The solute can then be located at the interface or in the oil or water microdomain (cf. Figure 9.9). Since three environments are available in ternary systems, the interface can be considered as a pseudo-phase or as a surfactant monolayer (37). 

A study of the solubilization of decanol in solutions of sodium octanoate showed that at low surfactant concentrations the solubilization of the additive increased rapidly after the cmc was exceeded, and continued to do so for some time as the concentration of sodium chloride was increased. At higher surfactant concentrations, however, it was found that there was an initial increase in decanol incorporation, which reached a maximum and then began to decrease as the salt level continued to increase. When the octanoate concentration well exceeded the cmc, the addition of salt resulted in an immediate decrease in the ability of the system to incorporate the additive. Such complex interactions have been attributed to alterations in the thermodynamics of mixed micelle formation for the decanol and carboxylate salt. Similar results may be seen in systems where the increased electrolyte content produces a change in the character of the micellar system a sphere-to-rod micellar transformation or the development of a mesophase, for example. 

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