436 JOURNAL OF COSMETIC SCIENCE 120 100 80 %weight 60 40 20 0 x iJ x & & & [] [] 5 10 Time (hours) Figure 5. Evaporation paths for water, lavender, and the two selected samples (S•, S 2) of the water/lavender oil/Tween 80 system. ', water I, lavender oil ', sample S1 x, sample S 2. For the evaporation study of the other system (water/Laureth 4/lavender oil), the com- position of the two selected samples are shown in Table II. The first sample was a one-phase microemulsion (sample S 3) with a composition of 41% water, 17% lavender oil, and 42% Laureth 4. The second sample was a two-phase emulsion (sample S4) with a composition of 80% water, 8% lavender oil, and 12% Laureth 4. The results show again that water is the fastest in evaporation, followed by S 4, then pure lavender oil, then S3. Water needed one hour to evaporate totally, lavender oil needed seven hours to reduce to 10% of its weight, S 4 took less than two hours to reduce to 20% of its weight, and S3 took seven hours to reduce to 80% of its weight and remained almost constant after that (Figure 6). It was found that S• lost more than 80% of its initial weight during the first five hours, while S 2 kept more than 40% of its weight after the same amount of time. In addition, after one hour, the weight lost was almost 40%, which was extended only 10% more after another four hours. On the other hand, S 2 showed its potential to keep its weight better than pure lavender oil over time, which indicates the possibility of the interaction with surfactant at this selected ratio (Figure 5). For the second system, where Laureth 4 was used (Figure 2), for sample S3, which has a high surfactant content, the one phase lost only 10% of its weight after seven hours, its weight staying constant from one hour up to six hours. S4, which has a low surfactant content and a high water content, has an evaporation path similar to that of pure water it can lose 70% of its weight within one hour and 95% within six hours (Figure 6). It can be noticed here that the samples with average-to-low water content can dominate Table II The Percent Composition for Samples S• and S4 for the Evaporation Study of the Water/Lavender Oil/Laureth 4 System Sample Number of phases % Water % Lavender oil % Laureth 4 S• 1 41 17 42 S4 2 80 8 12

LAVENDER OIL/WATER/STABILIZER SYSTEMS 437 120 100 80 %weight 60 40 20 0 X X X X X X [] 0 2 4 6 8 Time(hours) Figure 6. Evaporation paths for water, lavender oil, and the two selected samples (S3, S4) of the water/ lavender oil/Laureth 4 system. •, water I, lavender oil ', sample S4 x, sample S 3. their compositions better than the water-rich samples. On the other hand, the presence of a high content of surfactant allows lavender oil to keep many of its compounds and to slow down its evaporation. That means that higher surfactant solutions evaporate more slowly and retain their weight. A long-term evaporation study over a period of days was conducted to see what really happens in the true formulations, as the important factor in any formula containing fragrance is the potential of keeping the initial composition in an accepted ratio of the fragrance during evaporation (20,21). To demonstrate this effect, a room-temperature evaporation was performed over several days and the Laureth 4 system was chosen (Figure 2). The composition samples are shown in Table III, where the percentage of water is increased from A to E. For a large quantity of the water/Laureth 4/lavender oil system (5 g), evaporation was done at room temperature for some samples over several days. The compositions of these samples are shown in Table III, while the evaporation behaviors are clarified in Figure 7, which shows that over a period of ten days the fastest evaporation was for water, then sample E, sample D, sample C, pure lavender oil, sample B, and finally sample A. As shown in Figure 7, if the evaporation pathway went in the direction of the decreasing water content, the weight-decreasing pattern should be: sample E, followed by D, C, B, A, and finally pure lavender oil. Keeping in mind the effect of the surfactant and the percentage of lavender oil in these samples, this relation between the vapor pressure of the fragrance compounds and the amphiphilic association structures where these corn- Table Ill The Percent Composition for Samples for the Water/Lavender Oil/Laureth 4 System at Room Temperature Evaporation Sample Number of phases % Water % Lavender oil % Laureth 4 A 1 2.0 32.5 65.5 B 1 8.0 20.0 72.0 C 1 17.0 14.0 69.0 D 2 30.0 40.0 30.0 E 2 45.0 45.0 10.0