Microemulsions solubilization

Curcumin Tween 20/Glycerol monooleate/Medium chain triglycerides/water Multiple layer nanoemulsions Microemulsion Solubilization and dispersion in food systems [183]... 

Fig. 13 Effect of electrolyte concentration on Winsor microemulsion type (saliniu scan), w water o oil m microemulsion solubilization parameter volume of oil solubilized per mass of surfactant.

C. A. Miller, Micellar systems and microemulsions Solubilization aspects, in Handbook of... 

Miller, C.A., Micellar systems and microemulsions solubilization aspects, in Handbook of Surface and Colloid Chemistry, 1st edn., Birdi, K.S. (Ed.), CRC Press, Boca Raton, EL, 1997, p. 157. 

Lobo and co-workers (11) investigated the influence of oil (in the micellar environment) on the stability of foam. Two different types of emulsified oil systems were studied, i.e. (a) a microemulsion (solubilized within the micelle), and (b) a macroemulsion system. It was found that in each case, the foam stability was affected by a completely different mechanism. In the case of (a), where the foam films containing oil is solubilized within the micelle to form a microemulsion, the normal micellar interactions are changed. It had been earlier demonstrated that micellar structuring causes a step-wise thinning due to layer-by-layer expulsion of the micelles and such as effect was found to inhibit drainage and thus increase the foam stability. 

Uses Cosurfactant, solvent for active ingreds. in cosmetic anhyd. microemulsions solubilizer, efficacy booster for cosmetics including self tanning products, antiper-spirants, antimicrobial soaps, nail polish removers, hair care, skin care, sun care, toiletries... 

Micelles are mainly important because they solubilize immiscible solvents in their cores. Nonnal micelles solubilize relatively large quantities of oil or hydrocarbon and reverse micelles solubilize large quantities of water. This is because the headgroups are water loving and the tailgroups are oil loving. These simple solubilization trends produce microemulsions (see section C2.3.11). 

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

It is of particular interest to be able to correlate solubility and partitioning with the molecular stmcture of the surfactant and solute. Likes dissolve like is a well-wom plirase that appears applicable, as we see in microemulsion fonnation where reverse micelles solubilize water and nonnal micelles solubilize hydrocarbons. Surfactant interactions, geometrical factors and solute loading produce limitations, however. There appear to be no universal models for solubilization that are readily available and that rest on molecular stmcture. Correlations of homologous solutes in various micellar solutions have been reviewed by Nagarajan [52]. Some examples of solubilization, such as for polycyclic aromatics in dodecyl sulphonate micelles, are driven by hydrophobic... 

However, often the identities (aqueous, oleic, or microemulsion) of the layers can be deduced rehably by systematic changes of composition or temperature. Thus, without knowing the actual compositions for some amphiphile and oil of poiats T, Af, and B ia Figure 1, an experimentaUst might prepare a series of samples of constant amphiphile concentration and different oil—water ratios, then find that these samples formed the series (a) 1 phase, (b) 2 phases, (c) 3 phases, (d) 2 phases, (e) 1 phase as the oil—water ratio iacreased. As illustrated by Figure 1, it is likely that this sequence of samples constituted (a) a "water-continuous" microemulsion (of normal micelles with solubilized oil), (b) an upper-phase microemulsion ia equiUbrium with an excess aqueous phase, ( ) a middle-phase microemulsion with conjugate top and bottom phases, (d) a lower-phase microemulsion ia equiUbrium with excess oleic phase, and (e) an oA-continuous microemulsion (perhaps containing iaverted micelles with water cores). 

Microemulsions or solubilized or transparent systems are very important ia the marketing of cosmetic products to enhance consumer appeal (32,41). As a rule, large quantities of hydrophilic surfactants are required to effect solubilization. Alternatively, a combination of a solvent and a surfactant can provide a practical solution. In modem clear mouthwash preparations, for example, the flavoring oils are solubilized in part by the solvent (alcohol) and in part by the surfactants. The nature of solubilized systems is not clear. Under normal circumstances, microemulsions are stable and form spontaneously. Formation of a microemulsion requires Httle or no agitation. Microemulsions may become cloudy on beating or cooling, but clarity at intermediate temperatures is restored automatically. 

Solubilizing activity are also used in enhanced oil recovery. Tar and extremely viscous hydrocarbons are recovered by the injection of an aqueous solution of an anionic orthophosphate ester surfactant into a petroleum formation, retaining the surfactant in the formation for about 24 h, and displacing the solubilized hydrocarbons toward a recovery well. The surfactant forms an oil microemulsion with the hydrocarbons in the formation. An anionic monoorthophosphate ester surfactant which is a free acid of an organic phosphate ester was dissolved in water. The input of surfactant solution was 2-25% of the pore volume of the formation [250]. To produce a concentrate for the manufacture... 

By NMR, it has been observed that the solubilization of various diamagnetic salts in water/AOT/n-octane microemulsions induces a micellar reorganization that is dependent on the electrolyte valence and concentration [133]. 

Solubilization of biomolecules could induce change in the microemulsion structure. For example, in the presence of the human serum albumin and at low R value, the ternary microemulsion AOT/water/isoctane shows a transition to a bicontinuous microstructure [172],... 

As a result of the micellar environment, enzymes and proteins acquire novel conformational and/or dynamic properties, which has led to an interesting research perspective from both the biophysical and the biotechnological points of view [173-175], From the comparison of some properties of catalase and horseradish peroxidase solubilized in wa-ter/AOT/n-heptane microemulsions with those in an aqueous solution of AOT it was ascertained that the secondary structure of catalase significantly changes in the presence of an aqueous micellar solution of AOT, whereas in AOT/n-heptane reverse micelles it does not change. On the other hand, AOT has no effect on horseradish peroxidase in aqueous solution, whereas slight changes in the secondary structure of horseradish peroxidase in AOT/n-heptane reverse micelles occur [176],... 

In the case of myelin proteolipid solubilized in water/tetraethylene glycol monodo-decyl ether/dodecane microemulsions, its a-helical structure is preserved [176,177],... 

Even entrapment of entire cells within reversed micelles without loss of their functionality has been achieved. For example, mitochondria and bacteria (Actinobacter cal-coaceticus, Escherichia coli, Corynebacterium equi) have been successfully solubilized in a microemulsion consisting of isopropyl pahnitate, polyoxyethylene sorbitan trioleate [162], Enhanced hydrogen photoproduction by the bacterium Rhodopseudomonas sphaeroides or by the coupled system Halobacterium halobium and chloroplasts organelles entrapped inside the aqueous core of reversed micelles with respect to the same cells suspended in normal aqueous medium has been reported [183,184],... 

Solubilization of a graft copolymer comprising a hydrophobic poly(dodecyl-methacrylate) backbone and hydrophilic poly(ethylene glycol) monomethyl ether side chains in water/AOT/cyclohexane w/o microemulsions was rationalized in terms of the backbone dissolved in the continuous apolar phase and the side chains entrapped within the aqueous micellar cores [189],... 

Moreover, stable liquid systems made up of nanoparticles coated with a surfactant monolayer and dispersed in an apolar medium could be employed to catalyze reactions involving both apolar substrates (solubilized in the bulk solvent) and polar and amphiphilic substrates (preferentially encapsulated within the reversed micelles or located at the surfactant palisade layer) or could be used as antiwear additives for lubricants. For example, monodisperse nickel boride catalysts were prepared in water/CTAB/hexanol microemulsions and used directly as the catalysts of styrene hydrogenation [215]. 

Nanoparticles solubilized in w/o microemulsions have been obtained by performing in situ suitable reactions [196], by dispersion of particles [219,220], or by controlled nanoprecipitation of a solubilizate [221,222]. 

The application of microemulsions in foods is limited by the types of surfactants used to facilitate microemulsion formation. Many surfactants are not permitted in foods or only at low levels. The solubilization of long-chain triglycerides (LCTs) such as edible oils is more difficult to achieve than the solubilization of short- or medium-chain triglycerides, a reason why few publications on microemulsions are available, especially because food-grade additives are not allowed to contain short-chain alcohols (C3-C5). 

Amar, I., Aserin, A., and Garti, N., Solubilization patterns of lutein and lutein esters in food grade nonionic microemulsions, J. Agric. Food Chem., 51, 4775, 2003. 

Garti, N., Aserin, A., and Fanun, M., Non-ionic sucrose esters microemulsions for food applications. Part 1. Water solubilization. Colloid Surface A, 164, 27, 2000. 

The rates of multiphase reactions are often controlled by mass tran.sfer across the interface. An enlargement of the interfacial surface area can then speed up reactions and also affect selectivity. Formation of micelles (these are aggregates of surfactants, typically 400-800 nm in size, which can solubilize large quantities of hydrophobic substance) can lead to an enormous increase of the interfacial area, even at low concentrations. A qualitatively similar effect can be reached if microemulsions or hydrotropes are created. Microemulsions are colloidal dispersions that consist of monodisperse droplets of water-in-oil or oil-in-water, which are thermodynamically stable. Typically, droplets are 10 to 100 pm in diameter. Hydrotropes are substances like toluene/xylene/cumene sulphonic acids or their Na/K salts, glycol.s, urea, etc. These. substances are highly soluble in water and enormously increase the solubility of sparingly. soluble solutes. 

Electrochemical redox studies of electroactive species solubilized in the water core of reverse microemulsions of water, toluene, cosurfactant, and AOT [28,29] have illustrated a percolation phenomenon in faradaic electron transfer. This phenomenon was observed when the cosurfactant used was acrylamide or other primary amide [28,30]. The oxidation or reduction chemistry appeared to switch on when cosurfactant chemical potential was raised above a certain threshold value. This switching phenomenon was later confirmed to coincide with percolation in electrical conductivity [31], as suggested by earlier work from the group of Francoise Candau [32]. The explanations for this amide-cosurfactant-induced percolation center around increases in interfacial flexibility [32] and increased disorder in surfactant chain packing [33]. These increases in flexibility and disorder appear to lead to increased interdroplet attraction, coalescence, and cluster formation. 

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