The phase inversion temperature method

At a certain temperature some emulsions formulated with non-ionic surfactants change their structure, namely from o/w to w/o emulsions [47]. This process is reversible, i.e. that cooling below this so-called PIT leads again to the formation of an o/w emulsion. Forming emulsions via the PIT method often leads to very fine and long-term stable emulsions with particle sizes below 1 pun [48]. The main requirement that needs to be fulfilled is the 

In an early work with cosmetic ingredients the phase behaviour of potential base systems was investigated [49]. Different ethoxylated fatty alcohols were used in combination with 

An alternative surfactant combination which is free of ethoxylated molecules is based on rapeseed sorbitol ester and sodium lauroyl glutamate [53]. Here, the phase inversion from a w/o- to an o/w-emulsion can be initiated by the addition of lauroyl glutamate, which is a hydrophilic surfactant, instead of using the temperature. Penetration studies for the release of Vitamin E from PIT emulsions in comparison with other formulation concepts have been performed [54]. It has been shown that the penetration of Vitamin E into the skin is better for a w/o-cream than a PIT emulsion. The free diffusion of Vitamin E might be hindered by the oil-water interface, which acts as a barrier around the oil droplets. 

Numerous cosmetic applications of PIT emulsions have been described in patent literature. In the area of skin and body care products, new concepts for sunscreen compositions with UV filters in the lipophilic phase have been proposed [55]. The application of sunscreens onto the skin is more comfortable using a spray applicator instead of using a cream. Because of their small particle size, PIT emulsions are ideal for this task, since they are sprayable and long-term stable. Another idea is to combine UV protection which acts against the harmful properties of sun exposition, with tanning actives for a healthy look [56]. This product can be used in an airbrush system. 

Thin and sprayable antiperspirant formations can be obtained by the PIT method [57]. They contain aluminium chlorohydrate, which is an active antiperspirant compound. The disclosed formulations are based on ethoxylated fatty alcohols in combination with an oil mixture and propylenglycol. After phase inversion the resulting particle size is in the range of 100-300 nm, which makes the product sprayable and long-term stable. A second approach with the same deodorant active describes alcohol-free PIT emulsions with cross-linking polymers [58]. 

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Izquierdo, P., Esquena, J., Tadros, T.F., Dederen, C., Garcia, M.J., Azemar, N. and Solans, C. (2002) Formation and stability of nano-emulsions prepared using the phase inversion temperature method. Langmuir, 18 (1), 26-30. 

T. Forster, F. Schambil, and W. Von Rybinski Production of Fine Dispersion and Long-Term Stable Oil-in-Water Emulsions by the Phase Inversion Temperature Method. J. Dispersion Sci. Technol. 13, 183 (1992). 

P. Izquierdo, J. Esquena, T.F. Tadros, J.C. Dederen, J. Feng, J. Garcia-Celma, N. Azemar, and C. Solans Phase Behavior and Nano-Emulsion Formation by the Phase Inversion Temperature Method. Langmuir 20, 6594 (2004). 

J. Allouche, E. Tyrode, V. Sadtler, L. Choplin, and J.L. Salager Simultaneous Conductivity and Viscosity Measurements as a Technique to Track Emulsion Inversion by the Phase-Inversion-Temperature Method. Langmuir 20, 2134 (2004). 

Forster, T., Schambil, F. and von Rybinski, W. (1992) Production of fine disperse and long-term stable oil-in-water emulsions by the phase inversion temperature method. /. Disp. Sci. Technol.,... 

Psathas, P.A., Janowiak, M.L., Garcia-Rubio, L.H. and Johnston, K.P. (2002) Formation of carbon dioxide in water miniemulsions using the phase inversion temperature method. Langmuir, 18(8), 3039 6. 

Mitsui, T., Machida, Y. and Harusawa, F. (1970) An application of the phase-inversion-temperature method to the emulsification of cosmetics. Bull. Chem. Soc. Jpn., 43, 3044. 

Forster, T.,Schambil, F. and Tesmann, H. (1990) Emulsification by the phase inversion temperature method The role of self-bodying agents and the influence of oil polarity. Int. J. Cosmet. Sci., 12,217. 

Formation and stability of nano-emulsions prepared using the phase inversion temperature method, Langmuir 18, 26-30 (2002). 

Izquierdo P, Esquena J, Tadros TF, Dederen JC, Feng J, Garcia-Cehna MJ, et al. Phase behaviour and nano-emulsion formation by the phase inversion temperature method. Langmuir 2004 20 6594-8. 

Allouche, J, Tyrode, E., Sadtler, V., Choplin, L., and Salager, J. -L. 2004. Simultaneous conductivity and viscosity measurements as a technique to track emulsion inversion by the phase-inversion-temperature method. Langmuir, 20, 2134-2140. 

The phase inversion temperature (PIT) method is helpful when ethoxylated nonionic surfactants are used to obtain an oil-and-water emulsion. Heating the emulsion inverts it to a water-and-oil emulsion at a critical temperature. When the droplet size and interfacial tension reach a minimum, and upon cooling while stirring, it turns to a stable oil-and-water microemulsion form. " ... 

The most frequent emulsiflcation using phase inversion is known as the PIT (Phase Inversion Temperature) method [81-83] and occurs through a temperature quench. This method is based on the phase behavior of nonionic surfactants and the correlation existing between the so-called surfactant spontaneous curvature and the type of emulsion obtained. 

There are other variations of this approach that involve the phase inversion temperature (PIT) (see Section 3.6.1). In one method an emulsion is formed at a temperature a few degrees lower than the PIT, where the interfacial tension is quite low and small droplets can be formed. The emulsion can then be quickly cooled. Another method uses a controlled temperature change to cause an emulsion to suddenly change from a coarse oil-in-water (O/W) emulsion, through a microemulsion phase, and into a fine water-in-oil (W/O) emulsion [432]. 

Four different emulsifier selection methods can be applied to the formulation of microemulsions (i) the hydrophilic-lipophilic-balance (HLB) system (ii) the phase-inversion temperature (PIT) method (iii) the cohesive energy ratio (CER) concept and (iv) partitioning of the cosurfactant between the oil and water phases. The first three methods are essentially the same as those used for the selection of emulsifiers for macroemulsions. However, with microemulsions attempts should be made to match the chemical type of the emulsifier with that of the oil. A summary of these various methods is given below. 

In summary, the HLB method is only an empirical approach which has made it possible to organize a great deal of rather messy information on emulsion preparation, in order to choose candidate surfactants in trial and error laboratory work for suitable emulsion selection. There are other surfactant selection methods such as the phase inversion temperature (PIT) and the hydrophilic-lipophilic deviation (HLD) methods used for the same purpose in the emulsion industry, but these are outside the scope of this book. 

Two methods may be applied for the preparation of nano-emulsions (covering the droplet radius size range 50-200 nm). Use of high-pressure homogenisers (aided by appropriate choice of surfactants and cosurfactants) or application of the phase inversion temperature (PIT) concept. 

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