18 JOURNAL OF COSMETIC SCIENCE Table I [3CD Minimum Content for Emulsion Stability Under Various Stress Conditions One week storage One month One week storage at Centrifugation at 25øC storage at 25øC 60øC at 4200 g •CD minimum (% w/w) for emulsion stability 0.05 0.25 0.50 0.25 ]0 0 0,1 1 lO lOO pc•rficte size ( •m } Figure 1. Typical granulometric profile of the emulsions containing a high •CD ratio and aged one week. interfactial area stabilized and, thus, decreases the average oil droplet diameter (see Figure 2). This feature is observed even when the [3CD content of the emulsion is above the quantity that can be solubilized in the aqueous phase (0.5% w/w for an emulsion containing 30% w/w of water) (9). Therefore, the [3CD in "excess" relative to the water content should play the role of emulsifier reservoir during and after the emulsification process. However, beyond 3% w/w, further increase of •CD percentage does not affect the average oil droplet diameter. In order to investigate this intriguing effect above the solubility limit, we carried out the complete separation of the cream and the water phase through centrifugation and filtration steps. Then, the concentration of the [3CD in the aqueous phase was checked. The level in the aqueous phase, which is negligible when the total [3CD concentration of this emulsion is kept below the 3% w/w threshold (see Figure 3), increases suddenly above this limit to about half the solubility value and reaches this level by further increase of the [3CD ratio in the emulsion. This result is to be linked to the pattern of the average oil droplet diameter already seen in Figure 2. We

[3CD-STABILIZED EMULSIONS 19 4O 35 • 30 2 •20 =15 ,•1o o o 1 2 3 4 5 6 7' 8 9 [I•CD] (% w/w) Figure 2. Effect of the [3CD ratio on the average droplet diameter of emulsions containing 30% w/w of water after one-week storage. assume that up to this concentration, [3CD is mainly in a complexed form that should be the active form. Beyond the concentration threshold, a part of the additional [3CD should remain as a solid because the continuous aqueous phase is already saturated in free oligosaccharide (see Figure 3). One can assume that the [3CD threshold depends on the complexation kinetics. There- fore, it should be possible to exceed this limit by a modification of the interfacial area, the emulsification temperature, or the duration of the blending. However, the present work was focused on the general properties of the [3CD emulsions, and no attempt was made to optimize the conditions of preparation. PARTICLES IN THE SOLID PHASE Centrifugation of these emulsions prepared with [3CD usually brings about the separa- tion of a lower solid phase, even when the emulsifier is introduced after complete solibilization in the aqueous phase. The formation and the precipitation of [3CD com- plexes, which is widely described in the bibliography (9), is likely to be the only explanation. Moreover, we did check that the solid precipitate cannot be solubilized in deionized water at 25øC. Although these facts are not a direct proof, one may consider that this is a proof of the complexation phenomenon. The average particle diameter in the solid phase is about 1 pm (see Figure 4). This is consistent with a secondary peak in this size range that is observed in the granulometric profiles of emulsions containing a