Microemulsions surfactants

W. T. Osterloh and M. J. Jante, Jr. Surfactant-polymer flooding with anionic PO/EO surfactant microemulsions containing polyethylene glycol additives. In Proceedings Volume, volume 1, pages 485 94. 8th SPE/DOE Enhanced Oil Recovery Symp (Tulsa, OK, 4/22-4/24), 1992. 

Ethoxylated fatty esters, emulsifiers, detergents, and dispersants, 8 710t Ethoxylated nonionic surfactants, microemulsions based on, 16 428 Ethoxylated surfactants, 24 142, 148 Ethoxylates, 24 149-151 Ethoxylation, fatty amines, 2 523 2-Ethoxypyridine, 21 104 Ethoxyquin, 10 854 13 42t, 51 2-Ethyl-1-butanol... 

Fig. 15.4 Schematic ternary-phase diagram of an oU-water-surfactant microemulsion system consisting of various associated microstructures. A, normal miceUes or O/W microemulsions B, reverse micelles or W/O microemulsions C, concentrated microemulsion domain D, liquid-crystal or gel phase. Shaded areas represent multiphase regions.

Anton RE, Salager JL (1990) Effect of the electrolyte anion on the salinity contribution to optimum formulation of anionic surfactant microemulsions. J Colloid Interface Sci 140 75-81... 

Emulsions are two-phase systems formed from oil and water by the dispersion of one liquid (the internal phase) into the other (the external phase) and stabilized by at least one surfactant. Microemulsion, contrary to submicron emulsion (SME) or nanoemulsion, is a term used for a thermodynamically stable system characterized by a droplet size in the low nanorange (generally less than 30 nm). Microemulsions are also two-phase systems prepared from water, oil, and surfactant, but a cosurfactant is usually needed. These systems are prepared by a spontaneous process of self-emulsification with no input of external energy. Microemulsions are better described by the bicontinuous model consisting of a system in which water and oil are separated by an interfacial layer with significantly increased interface area. Consequently, more surfactant is needed for the preparation of microemulsion (around 10% compared with 0.1% for emulsions). Therefore, the nonionic-surfactants are preferred over the more toxic ionic surfactants. Cosurfactants in microemulsions are required to achieve very low interfacial tensions that allow self-emulsification and thermodynamic stability. Moreover, cosurfactants are essential for lowering the rigidity and the viscosity of the interfacial film and are responsible for the optical transparency of microemulsions [136]. 

The first part of the book discusses formation and characterization of the microemulsions aspect of polymer association structures in water-in-oil, middle-phase, and oil-in-water systems. Polymerization in microemulsions is covered by a review chapter and a chapter on preparation of polymers. The second part of the book discusses the liquid crystalline phase of polymer association structures. Discussed are meso-phase formation of a polypeptide, cellulose, and its derivatives in various solvents, emphasizing theory, novel systems, characterization, and properties. Applications such as fibers and polymer formation are described. The third part of the book treats polymer association structures other than microemulsions and liquid crystals such as polymer-polymer and polymer-surfactant, microemulsion, or rigid sphere interactions. 

Lawrence, M.J. Surfactant microemulsions and vesicles as vehicles for drug delivery. Eur. J. Drug Met. Pharmacokin 1994, 3, 257-269. 

Figure 6. Schematic ternary phase diagram of an oil-water-surfactant microemulsion system. (Reproduced with permission from Ref. 63. Copyright 1988 M. Dekker.)...

Ionic surfactants with only one alkyl chain are generally extremely hydrophilic so that strongly curved and thus almost empty micelles are formed in ternary water-oil-ionic surfactant mixtures. The addition of an electrolyte to these mixtures results in a decrease of the mean curvature of the amphiphilic film. However, this electrolyte addition does not suffice to drive the system through the phase inversion. Thus, a rather hydrophobic cosurfactant has to be added to invert the structure from oil-in-water to water-in-oil [7, 66]. In order to study these complex quinary mixtures of water/electrolyte (brine)-oil-ionic surfactant-non-ionic co-surfactant, brine is considered as one component. As was the case for the quaternary sugar surfactant microemulsions (see Fig. 1.9(a)) the phase behaviour of the pseudo-quaternary ionic system can now be represented in a phase tetrahedron if one keeps temperature and pressure constant. 

Acosta, E., Szekeres, E., Sabatini, D.A. and Harwell, J.H. (2003) Net-average curvature model for solubilization and supersolubilization in surfactant microemulsion. Langmuir, 19, 186-195. 

Nilsson, P.G. and Lindman, B. (1982) Solution structure of nonionic surfactant microemulsions from NMR self-diffusion studies. /. Phys. Chem., 86, 271-279. 

VI.4. Solubilization in Solutions of Micelle-Forming Surfactants. Microemulsions... 

Microemulsions were first discovered empirically by Schulman, who found that the addition of a fourth component (often an alcohol) to an emulsion containing oil, water, and a surfactant led to the formation of a clear, apparently homogeneous phase. This additional component is usually called the co-surfactant. Microemulsions have been the subject of intense study in recent years, especially in view of their possible use in enhanced oil recovery. A typical recipe for forming a microemulsion is given in Appendix I. 

Quite original is the attempt to obtain porous materials, for example, from crystalline calcium carbonate (aragonite) similar to the natural material chalk of a certain porosity [192]. Another attempt was made to synthesize macro-porous aragonite with a structure similar to the cocco-spheres of certain marine algae [295]. For this purpose, oil-water-surfactant microemulsions supersaturated with calcium bicarbonate were obtained. The pore size was determined by the water and oil concentration ratio. Microemulsions were applied on the substrate of micrometersized polystyrene beads. Hollow spherical shells of finished structure were produced as a result of a rapid mineralisation. The authors suggest that such materials could gain widespread use in materitils chemistry. 

Silicone oils with amino groups have also been solubilized in ionic surfactant microemulsions [58]. Organic bases such as pyridine, picoline, isoquinoline, and piperidine have been solubilized in anionic and cationic microemulsions [59], as well as dialkyl phthalate ester oil [60] or diesel oil [61], but no EACN value was reported. 

Figure 4 shows the typical phase diagram for a nonionic surfactant microemulsion system containing Triton X-100, decanol, and H2O [37]. The isotropic region near the water corner shows the O/W structure, and an isotropic region on the right-hand side of the phase diagram shows the W/O structure. 

Kunieda, H., and Aoki, R. (1995) Effect of added salt on the maximum solubilisation in ionic-surfactant microemulsion. Langmuir, 12, 5795-5799. 

There are two additional types of chemical flooding systems that involve surfactants which are briefly mentioned here. One of these systems utilizes surfactant-polymer mixtures. One such study was presented by Osterloh et al. [72] which examined anionic PO/EO surfactant microemulsions containing polyethylene glycol additives adsorbed onto clay. The second type of chemical flood involves the use of sodium bicarbonate. The aim of the research was to demonstrate that the effectiveness of sodium bicarbonate in oil recovery could be enhanced with the addition of surfactant. The surfactant adsorption was conducted in batch studies using kaolinite and Berea sandstone [73]. It was determined that the presence of a low concentration of surfactant was effective in maintaining the alkalinity even after long exposures to reservoir minerals. Also, the presence of the sodium bicarbonate is capable of reducing surfactant adsorption. 

In Chapter 3, Ezrahi et al. (Israel) discuss the use of subzero temperature behavior of water in microemulsions as an analytical tool to enable better understanding of the interfacial behavior of the surfactant. Microemulsions are cooled to subzero temperatures and the water in the internal reservoir freezes. In the heating cycle the thawing of the water is measured. The authors critically discuss the problems related to the use of this technique and the advantages derived from it. 

S. Ajith and A.K. Rakshit 1995 Studies of mixed surfactant microemulsion systems Brij 35 with Tween 20 and sodium dodecyl sulfate, J. Phys. Chem. 99,14778-14783. 

Eanun, M. 2007 Conductivity, viscosity, NMR and diclofenac solubilization capacity studies of mixed nonionic surfactants microemulsions, J. Mol. Liq. 135 5-13. 

Fanun, M. Phase behavior, structure evolution and diclofenac solubilization studies on mixed nonionic surfactants microemulsions. In Colloid and Surface Research Trends. Fong, P.A. (Ed.), Nova Science Publisher, New York, 2007, pp. 107-146. 

Ajith, S. and Rakshit, A.K. 1995 Effect of NaCl on a nonionic surfactant microemulsion system, Langmuir 11 1122-1126. 

Microemulsion containing Brig 35 and l-heptanol as co-surfactants at 1% (v/v) water. Hexane, or hexane chloroform (70 30, v/v), or hexane ethyl aeetate (70 30, v/v), at diffeent water eontents. System containing hexane at diff ent ratios of water per mol surfactant. Microemulsion free co-surfactant system containing Span 60 and Tween 60 ... 

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