16 JOURNAL OF COSMETIC SCIENCE Therefore, [3CD should be used in the composition of some emulsions in the near future. Shimada et al. assume that [3CD, which has no effect on the surface tension at the air/water interface, stabilizes the emulsions through the formation of a layer of complexes at the oil/water interface (12). The purpose of this paper is to investigate paraffin oil/water emulsions stabilized by [3CD in order to promote the use of this new emulsifier in cosmetics. MATERIALS AND METHODS MATERIALS AND EMULSION PREPARATION Each batch (300 g) of emulsion was prepared as follows. The hydrated [3CD (Kleptose from Roquettes FrSres) and deionized water are stirred for 15 min with a propeller in a 600-ml stainless steel beaker thermostated at the temperature of emulsification through a water bath. The paraffin oil (Primol 352 from ESSO), warm at the same temperature, is poured into the beaker at a rate of 100 ml/min. Then, the speed of the blender is increased, taking care not to introduce air bubbles into the dispersion. The emulsion is homogenized for 15 min. The temperature of emulsification is usually 20øC, except when otherwise stated. STABILITY TESTS ON EMULSIONS A greasy layer appears at the top of the oil/aqueous phase mixture after stopping the homogenization when the experimental conditions are unfavorable to emulsification. In the other cases, three samples of emulsion are poured into a 3-ml glass tube and sealed. In order to investigate emulsion stability, the samples are submitted to various stresses: storage for a week at 25øC followed by centrifugation at 4200 g for 30 min storage for a month at 25øC storage for a week at 60øC. Then the emulsion breakdown (formation of a greasy layer) is checked visually. The nature of the continuous phase is investigated by a conductimetric method. DROPLET SIZE Before measurement, the emulsion is diluted in deionized water and the dispersion is slowly stirred in order to separate flocculated droplets. The average droplet diameter is measured using a Malvern Mastersizer light-scattering sizer. MEASUREMENT OF [3CD CONCENTRATION OF THE AQUEOUS PHASE The aqueous phase, separated by centrifugation (4200 g for 30 min), is filtered with a Merck Dynaguard-ME (0.2 lam) filter. The measure of the [3CD concentration in the clear aqueous phase is performed by Roquette Frbres, the [3CD supplier, by an HPLC method. RHEOLOGICAL PROPERTIES OF THE EMULSIONS A Carrimed CS 550-Rheo rheometer (cone diameter: 2 cm cone-plane angle: 1 ø) is used for measuring the flow threshold at 20øC, with a linear strain rise speed of 200 N/m2/

[3CD-STABILIZED EMULSIONS 17 min. The Helipath viscosity is measured with a Rotovisco Haake-RV100 System m500 fitted out with a Helipath system. RESULTS AND DISCUSSION EFFECT OF [3CD AND OF THE COMPONENTS ADDITION MODE Emulsions containing paraffin oil/water/•CD [47.5/50/2.5 (weight basis)] were prepared following five modes for the addition of components: ß [•CD and the paraffin oil mixture are stirred for 5 hours at 25øC before water addition. ß •3CD and water are stirred for 5 hours at 25øC before paraffin oil addition. ß [•CD and water are stirred for 15 rain at 25øC before paraffin oil addition. ß [•CD and water are stirred for 12 hours at 60øC and then 3 hours at 25øC before paraffin oil addition. ß [•CD is added to water at 25øC immediately before paraffin oil addition. In all cases, the continuous phase of the emulsions was the aqueous phase, oil separation was never observed, and the aqueous phase separated after seven days of storage at 25 øC was about 30% of the total emulsion weight. Therefore, we concluded that under these conditions and with the [•CD sample that we had used, emulsifying activity does not depend on the sequence for mixing the three components, water, oil, and [•CD. EFFECT OF TEMPERATURE ON EMULSION FORMATION In the literature, emulsions are usually prepared at high temperature for reducing oil viscosity. These experiments show that a paraffin oil/water/lBCD system cannot be emulsified if the temperature exceeds 53øC for a 70/29.5/0.5 w/w/w composition, and 83øC for a 70/26/4 one. Thus, the border temperature is linked to the cyclodextrin concentration. As the emul- sifter is supposed to be the [3CD complex and not the [3CD itself, these results may be linked to the decrease of the association constants between [3CD and its guests while the temperature is increased. EFFECT OF [•-CYCLODEXTRIN CONCENTRATION ON EMULSION FORMATION AND STABILITY Formulations containing 0.005% to 8% w/w of [3CD and 10% to 90% v/v of paraffin oil were emulsified at 20øC. The emulsions were always of the oil-in-water type, even when the phase addition sequence was inverted. The minimum [3CD ratio for paraffin oil emulsification was about 0.025% w/w. However, there is a major risk of emulsion breakdown during storage under various conditions when the [3CD concentration is below 0.5% w/w, as shown in Table I. This stability for such a low level of [3CD content, in comparison to the claims found in the patent literature, is a major characteristic of these three-component emulsions. The stability may be enhanced by the use of a fourth component (for example, a thickening agent) for limiting the creaming tendency of these emulsions (7,8). The granulometric profiles of the emulsions were obtained with the Malvern Mastersizer (see Figure 1). As expected, increasing emulsifier concentration enables us to increase the