Co-surfactant

Phospholipids are perhaps the common zwitterionic surfactants used in microemulsions. However, they are too lipophihc to be used alone and have a fairly high critical packing parameter, making their incorporation into microemulsions difficult (Moreno et al, 2003). If used, co-surfactants are also required to increase the fluidity of the interface (Gaonkar and Bagwe, 2002 Patel et al, 2006). 

Presently, no cationic surfactants (e.g., cetyl trimethylammonium bromide) are used in the manufacture of food-grade microemulsions. This class of surfactants is mostly used in industrial chemistry applications (Joshi and Mukheijee, 2(X)3 Zuev et al., 2004). 

The inherent properties of alcohol co-surfactants will impact on usage. In particular, alcohol chain length has a significant effect on the ionization of the surfactant and disorder at the oil/water interface. Thus, shorter-chained alcohols will increase interfacial disorder (flexibihty) (Bansal et al., 1979 Tabony et al., 1983). However, toxicity concerns limit the use of effective co-surfactants such as 1-butanol, 2-butanol and tcrt-butanol, which are toxic to humans (Attwood, 1994). The most conunonly used food-safe co-surfactant is ethanol, though its use in foods limits product marketing due to regulatory requirements, which differing from country to country. 

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For the separation of amino acids, the applicability of this principle has been explored. For the separation of racemic phenylalanine, an amphiphilic amino acid derivative, 1-5-cholesteryl glutamate (14) has been used as a chiral co-surfactant in micelles of the nonionic surfactant Serdox NNP 10. Copper(II) ions are added for the formation of ternary complexes between phenylalanine and the amino acid cosurfactant. The basis for the separation is the difference in stability between the ternary complexes formed with d- or 1-phenylalanine, respectively. The basic principle of this process is shown in Fig. 5-17 [72]. 

AOT, could form w/c RMs in the presence of the commercially available perfluoropentanol (F-pentanol) as a co-surfactant, and the RMs formed could provide polar micro-aqueous for highly ionic chemicals[4,5]. Herein, we present the synthesis of crystalline nanoparticles of Ag, Agl, and Ag2S (which have potential application as photoelectric and thermoelectric devices) in the polar micro-aqueous domains of the w/c RMs stabilized by the AOT/F-pentanol (AOTF) surfactant/co-solvent combination, suggesting the possibility of the commercial utilization of SCCO2 in nanomaterials synthesis. 

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 quantitative determination of surfactant concentration in solution is an essential part of any experimental work on surfactant adsorption or phase behaviour. In the field of experimental enhanced oil recovery the technique employed should be capable of determining surfactant concentrations in sea water, and in the presence of oil and alcohols, the latter being frequently added as a co-surfactant. 

While raising the pH gave some improvements in lather, more improvement was needed. Various co-surfactants, including alkyl sulfates, alkyl aryl sulfonates, and fatty acid taurides were effective in improving the speed of lather when present at levels of around 5%. Cost considerations led to choosing an alkyl aryl sulfonate, particularly sodium dodecyl benzene sulfonate, as it was already widely used in the formulation of laundry detergents. 

DR. THOMAS For a solute the meaningful thing is the degree of contact with the aqueous phase. In a small micelle the solute is close to or on the surface, and it is in contact with the water. In a larger microemulsion the molecule is in the oil, the other volume. However, depending on the solute, it may penetrate further into the micelle and you can then talk of the water or lipid side of the surface. We can control the location by use of a co-surfactant [Thomas, J. K. Chem. Rev., op. cit.]. 

The low interfacial tensions between two liquids have been measured for different systems by using the pendant drop method. In the case of the quaternary system Ci2ll25S 3 tNa+H20+n-Butanol+Toluene, the interfacial data as measured by pendant drop method are compared with reported literature data, using other methods (with varying NaCl concentration). In order to understand the role of co-surfactant, ternary systems were also investigated. The pendant drop method was also used for measuring the interfacial tension between surfactant-H20/n-alcohol (with number of carbon atoms in alcohol varying from 4-10). The interfacial tension variation was dependent on both the surfactant and alcohol. 

S. Marie Bertilla, J.L. Thomas, P. Marie, M.P. Krafft, Co-surfactant effect of a semi-fluorinated alkane at a fluorocarbon/water interface. Impact on the stabilization of fluorocarbon-in-water emulsions, Langmuir 20 (2004) 3920-3924. 

Temperature sensitivities can be a limiting factor when using surfactants in groundwater systems. Low temperatures can cause the surfactant concentration to drop below the cation exchange capacity (CMC), rendering the surfactant useless. This effect can be abated with surfactant engineering or by using a co-surfactant. 

The phase behavior of anionic-cationic surfactant mixture/alcohol/oil/ water systems exhibit a similar effect. First of all, it should be mentioned that because of the low solubility of the catanionic compound, it tends to precipitate in absence of co-surfactant, such as a short alcohol. When a small amount of cationic surfactant is added to a SOW system containing an anionic surfactant and alcohol (A), three-phase behavior is exhibited at the proper formulation, and the effect of the added cationic surfactant may be deduced from the variation of the optimum salinity (S ) for three-phase behavior as in Figs. 5-6 plots. Figure 16 (left) shows that when some cationic surfactant is added to a SOWA system containing mostly an anionic surfactant, the value of In S decreases strongly, which is an indication of a reduction in hydrophilicity of the surfactant mixture. The same happens when a small amount of anionic surfactant is added to a SOWA system containing mostly a cationic surfactant. As seen in Fig. 16 (left), the values of In S at which the parent anionic and cationic surfactant systems exhibit three-phase behavior are quite high, which means that both base surfactants, e.g., dodecyl sulfate... 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

Many reports are available where the cationic surfactant CTAB has been used to prepare gold nanoparticles [127-129]. Giustini et al. [130] have characterized the quaternary w/o micro emulsion of CTAB/n-pentanol/ n-hexane/water. Some salient features of CTAB/co-surfactant/alkane/water system are (1) formation of nearly spherical droplets in the L2 region (a liquid isotropic phase formed by disconnected aqueous domains dispersed in a continuous organic bulk) stabilized by a surfactant/co-surfactant interfacial film. (2) With an increase in water content, L2 is followed up to the water solubilization failure, without any transition to bicontinuous structure, and (3) at low Wo, the droplet radius is smaller than R° (spontaneous radius of curvature of the interfacial film) but when the droplet radius tends to become larger than R° (i.e., increasing Wo), the microemulsion phase separates into a Winsor II system. 

In order to improve the luminescence behaviors and obtain better quantum yields, Zhang et al. [245] have suggested a reflux treatment by diluting w/o microemulsions of CdS nanoparticles with the same w/o microemulsions but substituting the reactant solution with H2O. The water in the w/o microemulsion droplets was removed by the co-surfactant (n-hexanol), the trap sites on the nanoparticle surface decreased improving the crystalHnity and thus the fluorescence efficiency. 

Co-solvent is a type of solvent (also termed as co-surfactant) which can help surfactants dissolve in the organic solvent and form RMs thereafter. Although the... 

In order to be exploitable for extraction and purification of proteins/enzymes, RMs should exhibit two characteristic features. First, they should be capable of solubilizing proteins selectively. This protein uptake is referred to as forward extraction. Second, they should be able to release these proteins into aqueous phase so that a quantitative recovery of the purified protein can be obtained, which is referred to as back extraction. A schematic representation of protein solubilization in RMs from aqueous phase is shown in Fig. 2. In a number of recent publications, extraction and purification of proteins (both forward and back extraction) has been demonstrated using various reverse micellar systems [44,46-48]. In Table 2, exclusively various enzymes/proteins that are extracted using RMs as well as the stability and conformational studies of various enzymes in RMs are summarized. The studies revealed that the extraction process is generally controlled by various factors such as concentration and type of surfactant, pH and ionic strength of the aqueous phase, concentration and type of CO-surfactants, salts, charge of the protein, temperature, water content, size and shape of reverse micelles, etc. By manipulating these parameters selective sepa-... 

Alcohol (co-surfactant) Negative until < h, otherwise positive influence of the hydrophilic (Oo) and hydrophobic (y part of the co-surfactant on the resulting main curvature... 

Micelles are spontaneously formed by most surfactants (especially single-chained ones) even at fairly low concentrations in water, whereas at higher surfactant concentrations, with or without the addition of an oil (e.g. octane) or co-surfactant (e.g. pentanol), a diverse range of structures can be formed. These various structures include micelles, multibilayers (liquid crystals), inverted micelles, emulsions (swollen micelles) and a range of microemulsions. In each case, the self-assembled structures are determined by the relative amounts of surfactant, hydrocarbon oil, co-surfactant (e.g. pentanol) and water, and the fundamental requirement that there be no molecular contact between hydrocarbon and water. 

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