EMULSION SYSTEM EVAPORATION 27 0.03 7 t2b0.02 0 00 DECANE Isotropic Liquid 3-Phas• 2-phasc ,&tea Lameliar Liquid fl O O. 1 0.2 0.:1 Q,I 0 5 O.fi 0.7 (1 fl (1.9 w^R Composkion Prackon ISOSTEARIC ACID/TRIETHANOLAMINE I 0 65/35 Figure 2. In the phase region in the plane investigated were three isotropic solutions: water, decane, and a decane solution of the emulsifier combination with small water solubilization and a lamellar liquid crystal. The three-phase region (Figure 4), aqueous solution, decane solution, and the lamellar liquid crystal covered a large area. The black parts illustrate the strong reduction in the evaporation rates. showed the reduction of the evaporation rate to correspond to the appearance of the lameliar phase. With this in mind, the breaking point of the evaporation curve was determined geometrically. Its projection is ma. rked on the ternary phase diagram. This breaking point corresponded to the compositior• at which a sudden change in rate was noticed. The results are shown in Figure 2, and are in good agreement with the boundary of the three-phase region determined by optical microscopy. This way a straightforward connection between the evaporation rate and the presence of a lameliar phase was established. On the other hand, there appeared to be no correlation between the time at which the evaporation rate was suddenly reduced and the W/O ratio of the emulsion. Finally, a change in the rate of evaporation was detected for compositions lying between 0.46 and 0.75, as shown on Figure 2. However, these changes were not as conspicuous as in the first case, but in good agreement with the compositions giving a lameliar phase as the only phase. DISCUSSION The results clearly demonstrated the relation between the mesomorphic structures that

28 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DECANE 0.03 c•O 02 0 00 ---1 I --.I I I ISOSTEARIC ACID/TRIETHANOLAMINF. 0 0 0 I 0 2 0 3 0 4 0 5 0 G 0.7 0 8 O 9 ! 0 65/35 w^'ra Cornposi I.io lVrac[ion Figure 3. The evaporation rates were strongly reduced where the lameliar liquid crystal appeared in the composition (Figure 2). occurred when composition of the system changed and the corresponding evaporatio rate. In our preceding article (7), we focused our attention on the coalescence and flocculatio of oil and water droplets within the emulsion, when it was spread as a thin film. For that purpose, a very small amount of emulsifier was used (2% on total weight), and the concentration of the surfactant remained sufficiently low for a liquid crystal to enter the composition first at a late stage. Hence its effect on the evaporation rate could not be observed. In the present article, the liquid crystalline structure of the emulsifier has a significan influence, because, with reduction of water and decane content, the composition passes through a multi-phase system containing a large amount of the lameliar phase during evaporation at an early stage. Such results have already been discussed by Lochhead (8), where a change of evaporation rate from an initial rapid rate followed by a lower rate could be related, by means of optical microscopy, to the presence of large amounts of a liquid crystalline phase. The present more complicated system merits an analysis of developments leading to the appearance of the lameliar phase. As we look at the complete phase diagram of the system (9), the starting material consists of two isotropic liquid phases in equilibrium. One of these is water with a small