VITAMIN C AND SDS/PENTANOL/WATER SYSTEM PENTANOL rTER I A9CORIIICAaD □ -0% 0- 2% � -10",{, ■ -20% ■ -&0% sos 269 Figure 1. Solubilization of ascorbic acid in a microemulsion region formed by water, pentanol, and SDS. Table I Composition (Percentage by Weight) and Type of the Examined Samples 1-pentanol H20 Microemulsion type (wt%) (wt%) (wt%) 89 5 W/0 77 17 W/0 75 19 W/0 65 29 W/0 50 44 W/0 39 55 W/0 22 72 Bicontinuous system 7 87 0/W 5 89 0/W 3 91 0/W 93 0/W 0 94 Micellar solution In all samples the SDS content was 6% by weight. They concluded that alkanoyl-6-O-ascorbates are more stable in surfactant aggregates than in the aqueous solution. The systems mentioned above contain many ingredients that improve their properties. They are rather not suitable for basic studies. We propose as the model system that consisting of SDS, pentanol, and water. The first reason for investigating this system is that it contains a very well pronounced microemulsion region (18,36,37). This region includes an inverse micellar solution, which is the basis for W /0 microemulsions, a bicontinuous part, and the aqueous micellar solution that forms the basis for the O/W microemulsions. The second reason is that ascorbic acid can be solubilized up to 60% by weight into a microemulsion (18). Therefore, in our opinion, this system can serve as a model for studying an effect of AA on the rheological properties of various types of microemulsion. Understanding the rheology of the antioxidant-containing emulsions is useful not only

270 JOURNAL OF COSMETIC SCIENCE 0.014 ---------�- - � - · -·� - 0.012 :' 0.008 l J 0.006 0.004 o,._ __________________________________ ......,. 0 10 20 30 40 50 60 70 80 90 100 Water Content In Mlcroemulsion [%wt] Figure. 2. Influence of temperature on the viscosity of the microemulsion region of the SDS/pentanol/water system. Temperature 15°c 22°c 30°c 40°C Table II Temperature Influence on Viscosity of Water Data 1 (mN · s/m2) (mPa · s) 1.404 0.958 0.807 0.656 Data 2 (mN · s/m2 ) (mPa · s) 1.005* 0.801 0.656 * 20°C: data 1---(40) data 2---(41) data exp.-measured values. Data exp. (mN · s/m2) (mPa · s) 1.11 0.931 0.812 0.664 in various pharmaceutical and cosmetic formulations, where processing variables can result in a change of dispersed phase volume, size distribution, and particle-particle interaction as well as particle deformability, but also in studying the naturally occurring processes. Micelles can be considered as a simple model of the cell membranes present in the biological system (18,25,38,39). EXPERIMENT AL The sodium dodecyl sulphate, L-ascorbic acid, and 1-pentanol used were supplied by Fluka Chemie and RdH Laborchemicalien GmbH & Co. KG. Water was doubly redis­ tilled.