Mixing microemulsions

By decreasing the amount of APG while increasing the GMO weight fraction, a liquid crystalline/microemulsion mixed phase is obtained. In the 40% water case, at even higher GMO weight fractions, a pure liquid crystalline phase is observed. For 65% water no pure liquid crystalline phase is seen, and the system becomes unstable and phase separates. For 90% water a finely dispersed emulsion with a bluish shine is observed at higher GMO weight fractions the surfactant system becomes too lipophilic to stabilize the system and, consequently, phase separation occurs. 

The concept of microemulsions now holds a central role within the field of surfactant technology. Perhaps the most fundamental fact captured by the term is that, contrary to a popular saying, oil and water can mix. 

The term microemulsion was introduced by Schulman, who studied surfactant solutions as eady as 1943 (22). At that time it was widely accepted that "oil and water do not mix," and Schulman understood that an emulsion scatters light because it contains droplets whose diameters are large compared to the wavelength of light (see Emulsions). Thus, the term y /mJemulsion implies a system which (like an emulsion) contains droplets of oil or water, but in which the droplets are too small to scatter light. 

When comparable amounts of oil and water are mixed with surfactant a bicontinuous, isotropic phase is formed [6]. This bicontinuous phase, called a microemulsion, can coexist with oil- and water-rich phases [7,1]. The range of order in microemulsions is comparable to the typical length of the structure (domain size). When the strength of the surfactant (a length of the hydrocarbon chain, or a size of the polar head) and/or its concentration are large enough, the microemulsion undergoes a transition to ordered phases. One of them is the lamellar phase with a periodic stack of internal surfaces parallel to each other. In binary water-surfactant mixtures, or in... 

Micro emulsions based on a heparin-chitosan complex suitable for oral administration based on ingredients acceptable to humans were studied with or without biologically active ingredients. Appropriate mixing and modifications of these microemulsions lead to nanometer-sized heparin-chitosan complexes [108]. 

Different methods are used in microemulsion formation a low-energy emulsification method by dilution of an oil surfactant mixture with water and dilution of a water-surfactant mixture with oil and mixing all the components together in the final composition. These methods involve the spontaneous formation of microemulsions and the order of ingredient addition may determine the formation of the microemulsion. Such applications have been performed with lutein and lutein esters. ... 

The high sulfur-containing feedstock and the biocatalyst, usually suspended in the aqueous phase have to be contacted with each other in a bioreactor. A homogeneous, continuous phase would be preferred, which would imply formation of an emulsion, preferably a microemulsion. Several bioreactor designs have been suggested for biodesulfurization of petroleum feedstocks including impeller-mixed systems [65,202], electro-spray bioreactor [220,261,262], and draft tube air-lift bioreactor [263],... 

As outlined in Chapter 5, Section 5.2.3.2 various approaches to overcoming the low rates of the hydroformylation of long chain alkenes in aqueous biphasic systems have been proposed. Some of these, such as the use of microemulsions [24-26] or pH dependent solubility [27], have provided improvements often at the expense of complicating the separation process. Perhaps the most promising new approaches involve the introduction of new reactor designs where improved mixing allows for... 

A. Martinez-Arias, M. Femandez-Garcia, V. Ballesteros, L.N. Salamanca, J.C. Conesa, C. Otero and J. Soria, Characterization of high surface area Zr-Ce (1 1) mixed oxide prepared by a microemulsion method, Langmuir 15,4796-4802 (1999). 

As for direct emulsions, the presence of excess surfactant induces depletion interaction followed by phase separation. Such a mechanism was proposed by Binks et al. [ 12] to explain the flocculation of inverse emulsion droplets in the presence of microemulsion-swollen micelles. The microscopic origin of the interaction driven by the presence of the bad solvent is more speculative. From empirical considerations, it can be deduced that surfactant chains mix more easily with alkanes than with vegetable, silicone, and some functionalized oils. The size dependence of such a mechanism, reflected by the shifts in the phase transition thresholds, is... 

Several approaches have been proposed toward gaining a better degree of mixing and lowering the temperature necessary for complete crystallization. These encompass the methods of spray-drying[5], freeze-drying[6], coprecipitation[7], microemulsion[8], citrate... 

As is often the case, we have become involved in microemulsions somwehat by accident. In the last five years or so we have been making systematic studies of the thermodynamic properties of aqueous organic mixtures and of electrolytes in these mixed solvents. Of particular interest were our heat capacity measurements. With a differential flow microcalorimeter it is possible to... 

In the water-flooding process, mixed emulsifiers are used. Soluble oils are used in various oil-well-treating processes, such as the treatment of water injection wells to improve water injectivity and to remove water blockage in producing wells. The same method is useful in different cleaning processes with oil wells. This is known to be effective since water-in-oil microemulsions are found in these mixtures, and with high viscosity. The micellar solution is composed essentially of hydrocarbon, aqueous phase, and surfactant sufficient to impart micellar solution characteristics to the emulsion. The hydrocarbon is crude oil or gasoline. Surfactants are alkyl aryl... 

The interactions between drugs and proteins such as albumin, acidic glycoprotein, and other possible target proteins are discussed in specific chapters. Some important applications of ACE concerning drug carrier systems (simple and mixed micelles, microemulsions, liposomes) are covered in subsequent chapters of this book. 

Separation of antibiotics and cephalosporins can be achieved successfully by CZE because most of them are ionic species. As an alternative to CZE, antibiotics and cephalosporins have been separated by MEEKC. The separation of cephalosporins in different systems (micelles, mixed micelles, and microemulsions) was investigated. The best separation was achieved in microemulsions (Fig. 4). Figure 4 shows that cephalosporins have better affinity to ME in the ME systems than in the MC systems. The affinity of cephalosporins in the ME systems decreases with decrease in the migration time. The MEEKC was also particularly suitable for neutral cephalosporins that could not be separated by CZE or MEKC (14) (see Fig. 5). The method provided good reproducibility and rapid separation with high efficiency. 

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