260 JOURNAL OF COSMETIC SCIENCE Figure 6. Microphotograph of the formula with Abil EM 90 5% at 60øC. surfactant recommended for use at 2.5 % with no complementary surfactants or additives (15). One of the aims of this work was to find a vehicle for Aloe vera in a suitable excipient that would both protect it and release it gradually. We therefore added Aloe vera at 2% to the two latexes with the best properties in the above studies (Table III). The timing of the incorporation of Aloe vera during the mixing process is crucial, as it can affect its diffusion in the excipient. The two variables during preparation were: 1. The gradual incorporation of Aloe vera into the prepared latex by continuous stirring to homogeneity. 2. Adding Aloe vera to the aqueous phase of the silicone latex and then incorporating that in the oily phase slowly and stirring continually. Nevertheless, whichever of the above two techniques is used, the most important vari- 10000 90OO 8OOO 7000 • 6000 ,-• 5000 o ß • 4000 3000 2000 1000 0 5 10 15 20 25 30 35 11sec Figure 7. Viscosity curves of the two preparations as a function of temperature: Abil EM 90 at 20øC ( ß ), Abil EM 90 at 30øC (&), Abil EM 90 at 40øC ('), Abil WE 09 at 20øC (O), Abil WE 09 at 30øC (/•), and Abil WE 09 at 40øC (,•).

SILICONE VEHICLES FOR ALOE VERA 261 700 600 500 400 300 200 lOO o 5 lO 15 20 25 30 35 11sec Figure 8. Fluidity curves of the two preparations as a function of temperature: Abil EM 90 at 20øC (•), Abil EM 90 at 30øC ('), Abil EM 90 at 40øC (I), Abil WE 09 at 20øC (¸), Abil WE 09 at 30øC (/•), and Abil WE 09 at 40øC ([•). able is the stirring process to obtain a suitable preparation. We recommend vigorous stirring at least at 2000 rpm (Eurostar Ika Labortechnik). The release study was performed next to observe the influence of the type of surfactant and the preparation technique on the faster or slower release of Aloe vera. The results of the four preparations (Figure 9) show that Abil WE 09 preparations release more Aloe vera. In contrast, Abil EM 90 has a more prolonged release, as is to be expected, since this surfactant is more powerful and therefore retains the Aloe vera longer. The method of incorporating Aloe vera in the preparation has also been observed to influence its subsequent release, which can be explained by the mechanism of action of these silicone surfactants. Due to the flexibility of the siloxane bonds and the size of these molecules, they do not form monomolecular layers on the droplets as occurs with classic surfactants. Instead, they trap the component for which they have the least affinity (the aqueous phase) within a three-dimensional structure (16). For this to take place, the Table III Addition of Aloe vera to the Two Latexes With the Best Properties Formulation 7 Formulation 8 DC 245 23% 23% n-decane 0.3 % 0.3 % Aloe vera 2% 2% H20 69.7% 69.7% Abil EM 90 5% -- Abil WE 09 5%