Nonionic surfactant discussion, phase diagrams

The influence of a cream containing 20% glycerin and its vehicle on skin barrier properties has been investigated. Recent studies have shown that polymers offer several advantages and can be used in skin care products. Phase diagrams were determined for lactic and isohexanoic hydroxy acids as well as salicylic acid with water, a nonionic surfactant and a paraffinic oil, to outline the influence of hydroxy acids on the structure in a model for a skin lotion. The results showed the influence of the acid to be similar to that of the oil but that the difference in chain length between the two alpha acids had only insignificant influence. The results are discussed from two aspects the structures involved in the lotion as applied, and the action of the lotion residue on the skin after the evaporation of the water. 

On the contrary, this set of experimental results would provide some ground for a theoretical and thermodynamical explanation of the evolution swollen micelle-microemulsion. Indeed each type of structure seems to reflect a domination of one or other component of the free energy of these nonionics at room temperature. Although a calculation and a discussion of these energy effects are well beyond the scope of the present paper, we can point out the importance of the forces specific to the hydrocarbon chain and to the oil beside the pure hydration forces. Van der Waals forces would favour the formation of a water layer, while entropic effects seem very important as far as the transitions hank-lamella and lamella-globule are concerned. These effects due to the solvent concentration (but also to the nature of the oil (2,5) are quite evident from the fine evolution of the phase diagrams, especially for water/surfactant ratios in the range 0.5-1.2. 

The phase behavior of diglycerol fatty acid esters (C G2, m = 12, 14, and 16) in liquid paraffin oil, squalane, and squalene is discussed. This section compares the nonaqueous phase behavior of mono- and diglycerol-based nonionic surfactants in different oils. Phase diagrams of surfactant/oil binary systems for the C ,G2 (m = 12-16) surfactants in a wide range of temperature and concentration at atmospheric pressure are shown in Figure 2.2. Gontrary to the G G) surfactants, the G ,G2 surfactants form a variety of self-assembled structures in nonpolar oils liquid paraffin oil, squalane, and squalene. 

Alexandridis et al. (2000) identified all the structures discussed above on a water/oil/PEO-PPO-PEO phase diagram. Because the solutions in many parts of the phase diagram are very viscous for these polymeric surfactants, further lowering of the temperature makes it very difficult to equilibrate the system. As a result, very often full temperature dependence is not reported, and has not been reported by Alexandridis et al. (2000). However, for these nonionics it is important to consider temperature dependence because of the changes it brings to the EO groups. Thus an additional effect of cloud point should also exist at low temperatures in this system. 

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