NEW NON-IONIC SURFACE ACTIVE AGENTS 273 ACKNOWLEDGEMENTS We are grateful to Dr. T. Abe and Mr. H. Nagasawa for their collaboration on our study, and to Mr. H. Futagoishi, Executive Director of Kanebo, Ltd., and Mr. M. Yamagishi, Manager of our Laboratory, who permitted the submission of this paper. REFERENCES (1) N. Ohba, Hydrophile-lipophile balance values for oil-water emulsions stabilized by nonionic surfactants. I. Hydrophile-lipophile balance values of nonionic surfactants determined by emulsifica- tion, Bull. Chem. Soc. Jpn., 35, 1016-20 (1962). (2) A. Tsugita, Y. Nishijima and T. Sasaki, Stable emulsion regions of surfactant-oil-water and surfactant-oil-water-long chain alcohol systems, Yukagaku, 29, 227-33 (1980). (3) J. H. Draize, Appraisal of the safety of chemicals in foods, drugs and cosmetics, Assoc. Food & Drug O•cials, U.S. 46-53 (1959). (4) B. Magnusson and A.M. Kligman, The identification of contact allergens by animal assay. The guinea pig maximization test,J. Invest. Dermatol., 52, 268-76 (1969). (5) K. F. Kuhlman, D. M. Grant and R. K. Harris, Nuclear Overhauser effects and carbon-13 relaxation times in •3C-(H) double resonance spectra,J. Chem. Phys., 52, 3439-48 (1970). (6) J. R. Lyerla, Jr., H. M. Mcintyre and D. A. Torchia, Carbon-13 nuclear magnetic resonance study of alkane motion, Macromolecules, 7, 11-4 (1974). (7) MOD ©, product of The Shin-ei Kagaku Co., Ltd., 1-19 Doshomachi, Higashi-ku, Osaka, Japan.

j. Soc. Cosmet. Chem., 32, 275-285 (September/October 1981) Rheological properties of magnesium aluminum silicate/xanthan gum dispersions PETER A. CIULLO, R. T. Vanderbilt Company, Inc., 30 IVinfield Street, Norwalk, CT 06855 Received January 12, 1981. Presented at the SCC Annual Meeting, New York City, December 12, 1980. Synopsis The ability to modify the rheology of magnesium aluminum silicate (MAS) with various ORGANIC THICKENERS has long been known and used to advantage. The widely used MAS/ carboxymethylcellulose combination, for example, has been the standard stabilizing system in liquid makeups for a number of years. Use of xanthan gum with MAS is now shown to even further extend the versatility of this smectite mineral. Comparative evaluations demonstrate how minor inclusions of xanthan gum in MAS dispersions provide synergism in both viscosity and yield value. The ability to modify the THIXOTROPIC nature of MAS is also shown, allowing pseudoplastic behavior through small additions of xanthan gum. For the best balance of properties, the most generally useful range of MAS:xanthan gum ratios in practice will be 9:1 to 2:1. This combination should provide formulas with good viscosity stability and smooth flow characteristics. The excellent yield value possible suggests superior stabilization of suspensions and emulsions. The combination of these properties makes the MAS/xanthan gum system especially well suited to stabilizing all types of fluid suspensions, lotions, and makeup. INTRODUCTION The refined smectite mineral, magnesium aluminum silicate (MAS), has for decades been popularly used as a thickener, suspending agent, emulsion stabilizer, and general texture modifier in a number of industries. The observed rheological properties of MAS that account for its utility are well described by the popular '*house of cards" model for the aqueous colloidal structure of smectites. Once the MAS has bee•n well dispersed and exists as discrete platelets, according to this model, the weakly positive platelet edges are attracted to the negatively charged faces. This attraction, coupled with face-face electrostatic repul- sion, is sufficient to establish a cohesive cubic network. This network determines dispersion properties. In addition to imparting viscosity, it is • responsible for suspend- ing and segregating the internal phase of emulsions and suspensions. The amount of force required to disrupt this network determines the yield value. Shear exceeding the yield value produces reduced dispersion viscosity. Increasing shear gives decreasing viscosity, as with pseudoplastic materials. Cessation of shear allows displaced faces and 275