Nano-emulsions cosmetic

Nano-emulsions are attractive for application in personal care and cosmetics as well as in health care due to the following advantages ... 

The capacity of solubilizing compounds in the droplets of a nano-emulsion gives the possibility of developing applications, implying the transport of these compounds through a continuous phase in which they are insoluble. Pharmaceutical and cosmetic applications for which nonpolar compounds are solubilized in oil droplets dispersed in aqueous media would be typical, and other possible applications in food or agrochemical fields have also been described [1,2],... 

Although nano-emulsions are thermodynamically imstable systems, they may possess high kinetic stability. This property together with their transparent or translucent visual aspect and a viscosity similar to that of water makes them of special interest for practical applications. Nano-emulsions are used in the pharmaceutical field as drug delivery systems [8,17, 18,25,28-33], in cosmetics as personal-care formulations [2,4,6,7,10,19-21,23,24,27], in agrochemical applications for pesticide delivery [3,34,35], in the chemical industry for the preparation of latex particles [9,22,26,36-38], etc. In addition, the formation of kinetically stable liquid/liquid dispersions of such small sizes is of great interest from a fimdamental viewpoint. 

Nano-emulsions have found increasing use in many different applications. The advantages of nano-emulsions over conventional emulsions (or macroemulsions) are a consequence of their characteristic properties, namely small droplet size, high kinetic stability, and optical transparency. In addition, nano-emulsions offer the possibility of using microemulsion-like dispersions without the need for high surfactant concentrations. In the following, the most relevant applications of nano-emulsions in the chemical, pharmaceutical, and cosmetic fields are summarized. 

The transparent visual aspect of nano-emulsions with droplet sizes below 200 nm makes them especially attractive for application in cosmetics. Apart from the appearance, similar to that of microemulsions, other advantages of nano-emulsions for cosmetic applications are their kinetic stability, a droplet size that can be controlled, and the possibility to achieve improved active delivery. For all these reasons, nano-emulsions have attracted increasing interest in the cosmetic field, as reflected by the papers [8,10,106] and numerous patents [19-21,23,24,27,107-111] that have appeared in the last few years. Oil-in-water nano-emulsions with a droplet size lower than 100 nm have been described in patents as hair- and skin-care [19,21,23,24,107-109], makeup [110], and sunscreen [20,111] formulations. 

Within the last 30 years, micro emulsions have also become increasingly significant in industry. Besides their application in the enhanced oil recovery (see Section 10.2 in Chapter 10), they are used in cosmetics and pharmaceuticals (see Chapter 8), washing processes (see Section 10.3 in Chapter 10), chemical reactions (nano-particle synthesis (see Chapter 6)), polymerisations (see Chapter 7) and catalytic reactions (see Chapter 5). In practical applications, micro emulsions are usually multicomponent mixtures for which formulation rules had to be found (see Chapter 3). Salt solutions and other polar solvents or monomers can be used as hydrophilic component. The hydrophobic component, usually referred to as oil, may be an alkane, a triglyceride, a supercritical fluid, a monomer or a mixture thereof. Industrially used amphiphiles include soaps as well as medium-chained alcohols and amphiphilic polymers, respectively, which serve as co-surfactant. 

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