Transparency microemulsions

It was observed that the titration of a coarse emulsion by a coemulsifier (a macromonomer) leads in some cases to the formation of a transparent microemulsion. Transition from opaque emulsion to transparent solution is spontaneous and well defined. Zero or very low interfacial tension obtained during the redistribution of coemeulsifier plays a major role in the spontaneous formation of microemulsions. Microemulsion formation involves first a large increase in the interface (e.g., a droplet of radius 120 nm will disperse ca. 1800 microdroplets of radius 10 nm - a 12-fold increase in the interfacial area), and second the formation of a mixed emulsifier /coemulsifier film at the oil/water interface, which is responsible for a very low interfacial tension. 

Figure 3 Transparent microemulsion region at 23 C for various B246 concentrations.

The dilution procedure, first proposed by Schulman ( 7) has been improved by Graciaa (12). First, oil is added to a transparent microemulsion. The sample becomes milky and transparency is obtained again by adding alcohol (with a certain amount of water). This is repeated several times. The added alcohol is plotted versus the added oil. A linear plot indicates a constant composition of the added substances which constitute the microemulsion continuous phase. The validity criteria for dilution procedure is (13) ... 

Micromulse WIO. [Korman, Fox] Ingredient for forming stable w/o emulsions and transparent microemulsions. 

These AOT microemulsions are characterized by a high surfactant to monomer ratio, (2.5-3). If the amount of AOT is too low, the optically transparent microemulsions evolve towards turbid and unstable latexes during polymerization, due to a shift in the emulsion region of the phase diagram [55,56]. However, it should be noted that AM plays the role of a cosurfactant in these systems, owing to its surface-active properties, thus leading to an increase in the micellar stabilization capacities [48]. 

Chung, S.L., Tan, C.-T., Tuhill, I.M., and Scharpf, L.G. 1994. Transparent oil-in-water microemulsion flavor or fragrance concentrate, process for preparing same, mouthwash or perfume composition containing said transparent microemulsion concentrate, and process for preparing same. U.S. Patent 5283056, filed July 1, 1993, and issued Feb. 1, 1994. 

Microemulsions are transparent systems of two immiscible fluids, stabilized by an interfacial film of surfactant or a mixture of surfactants, frequently in combination with a cosurfactant. These systems could be classified as water-in-oil, bicontinuous, or oil-in-water type depending on their microstructure, which is influenced by their physicochemical properties and the extent of their ingredients. - SMEDDSs form transparent microemulsions with a droplet size of less than 50 nm. Oil is the most important excipient in SMEDDSs because it can facilitate self-emulsification and increase the fraction of lipophilic drug transported through the intestinal lymphatic system, thereby increasing absorption from the gastrointestinal tract. Long-chain and medium-chain... 

Figure 3 represents the percentage of surfactant(s) required for the formation of an AM-NaAMPS microemulsion as a function of the HLB number for different compositions of the monomer feed [30]. The curves delineate the transition between a turbid emulsion and an optically transparent microemulsion. The transition is sharp and can be easily detected by turbidimetry or visually. It can be seen that microemulsions are found in an HLB domain ranging between 8 and 11. The curves exhibit a minimum for an optimum HLB value, which increases as the content of ionic monomer in the feed increases. Note also the low surfactant concentration needed for the formation of clear systems (5.5% < min < 7.5%) in spite of the large proportions of monomers incorporated ( 22%). 

Ag-poly(butyl acrylate-co-styrene) nanocomposites were prepared by Yin et al. [410] where the silver nanoparticles were obtained from a microemulsion. An aqueous solution of AgN03 was added to a mixture of toluene, butylacrylate, styrene, sodium dodecyl sulfate and 2-hydroxy-a-methacrylate (HEMA). A transparent microemulsion formed after addition of Span 80 under stirring. This product was bubbled with N2 and irradiated with to y-ray source for 6h (the irradiation helped both polymerization of monomers and reduction of metal ions). Silver particles, collected after de-emulsification by acetone and water, had an average size of about 8.5 nm. 

Upon preparation, the multicomponent fluid systems were allowed to stand undisturbed at constant temperature for 3 days or until the resulting multiphase systems exhibited clear, transparent microemulsions and sharp interfaces. In all of these systems, the microemulsion phase contained virtually all of the sulfonate in the system. 

Due to their transparency, microemulsions represent a very attractive type of cosmetic formulation, e.g. hair styling gels, perfume gels, bath preparations, sunscreen gels, etc. Their main problem is the relatively high surfactant concentration required for their formulation compared with nano- and macroemulsions. Proper choice of the surfactant system used for their formulation is required to avoid any side-effects, e.g. skin irritation. To arrive at the optimum composition of microemulsion systems, one needs to the phase diagram for these multicomponent formulations. 

From the literature data it appears that the transparent microemulsion systems are prepared under following considerations ... 

A keen interest in microemulsions of fluorocarbons in water was kindled by the need for synthetic oxygen earners in blood (see Section 10.4). Gerbacia and Rosano [121] prepared a stable fluorocarbon emulsion using a mixture of fluorinated and hydrocarbon-type nonionic surfactants. The droplet size was not determined, however, and the emulsions were not characterized. Oliveros et al. [122] prepared perfluorinated microemulsions consisting of four components (1) sodium perfluorooctanoate, an anionic fluorinated surfactant (2) 2,2,3,3,4,4,4-heptafluoro-1-butanol (3) perfluorohexane (4) water. The pseudoternary-phase diagram (Fig. 4.40) shows two regions. Mi and Mi, of respective W/0 and OAV microemulsions [122]. These optically transparent microemulsions were characterized by nuclear magnetic resonance spectroscopy. 

Unlike the system with GMO, the formation of a broad microemulsion phase is not observed in the whole temperature range for the phase inversion in the model emulsion containing glyceryl monoisostearate (GMI) (Fig. 7) [10]. Instead, a finely dispersed bluish emulsion is formed at an alkyl poly-glycoside/GMI ratio of about 2 1. A transparent microemulsion can be observed only at temperatures above 50°C. The phase inversion concentration ratio does not vary with temperature. 

The model emulsion containing glyceryl monohydroxy stearate (GMHS) shows a different phase behavior. Apart from a distinct temperature dependence similar to the PIT phenomenon at concentration ratios between 2 8 and 7 3, no transparent microemulsion can be observed. 

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