SOLUBILITY PARAMETERS IN COSMETIC FORMULATING 333 (18) (19) (20) (21) (22) (23) (24) (25) (17) D. L. Wernick, Stereographic display of three dimensional solubility parameter calculations, Ind. Eng. Chem. Prod. Res. Der., 23, 2 (1984). J. D. Van der Waals, Z. Phys. Chem., 133 (1890). F. London, The general theory of molecular forces, Trans. Faraday Soc., 33, 8 (1937). R. F. Blanks and J. M. Prausnitz, Ind. Eng. Chem. Fund, 3, 1 (1964). W. H. Keesom, Leiden Comm. (1913), Proc. Akad. Wettemch. C. F. Boettcher, Theory of Electric Polarization (Elsevier, New York, 1952), Chapter 5. A. Beerbower and J. R. Dickey, ASLE Trans., 12, 1 (1969). B. F. Goodrich Inc., Specialty Polymers and Chemicals Division, Technical Data Sheet No. 41. A. Martin, P. L. Wu, and A. Beerbower, Expanded solubility parameter approach II., J. Pharm. Sci., 73, 188 (1984). (26) R. RawIs, Science: Chemists propose universal solubility equation, Chem. & Engr. News, March 18, 1985, p 20. (27) A. Beerbower, "The Environmental Capability of Lubricants," in An Interdisciplinary Approach to Liquid Lubricant Technology, P.M. Ku, Ed. (NASA Monograph SP No. 318, Washington, D.C., 1973), pp 365-431. (28) C. Hansch and T. Fujita, A method for correlation of biological activity and chemical structure, J. Am. Chem. Soc., 86, 1616 (1964). (29) A. Cammarata, S. J. Yau, and K. S. Rogers, Some biological applications of regular solution theory, Pure Appl. Chem., 35, 495 (1973). (30) H. Burrell, Pigment wetting parameter, Am. Chem. Soc. Div. Org. Coat. Plast., Paper 35(2), 18 (1975). (31) C. M. Hansen, Solvents for coatings, Chemtech, 2, 547 (1975). (32) C. M. Hansen, "Solvent Selection by Computer," in Solvents--Theory & Practice, Adv. Chem, Ser. 124, R. W. Tess, Ed. (Am. Chem. Soc., Washington, D.C., 1973), Chapter 14. (33) S. Ross and G. Nishioka, The relation of foam behavior to phase separations in polymer solutions, Colloid Polym. Sci., 255, 560 (1977). (34) A. Beerbower and M. W. Hill, Application of cohesive energy ratio (CER) concept to anionic surfactants, Am. Cosmet. Perfum., 87, 85 (1972). (35) H. Schott, Solubility parameter and hydrophilic-lipophilic balance of nonionic surfactants, J. Pharm. Sci., 73, 790 (1984). (36) J. Sevestre, On some corrections involving the solubility parameter, Double Liaison, 109, 67 (1964) (in French). (37) S. A. Siddiqui and H. L. Needles, Solubility parameters, Textile Research Journ., 52, 570-579 (1982). (38) G. Scatchard, Equilibria in non-electrolyte solutions, J. Am. Chem. Soc., 38, 321 (1916). (39) J. H. Hildebrand, Solubility, J. Am. Chem. Soc., 38, 1442-1473 (1916). (40) H. Burrel, Solubility parameters, Interchem. Rev., 14, 3-16 (1955). (41) H. Lee, Relation between solubility parameters and surface tension, J, Paint Technol., 42, 365-370 (1970). (42) D. D. Lawson and J. D. Ingham, Method for estimating solubility parameter, NASA Tech. Brief, TSP73-10022 (1973). (43) A. W. Francis, Critical Solution Temperatures, Adv. Chem. Ser. 31 (Am. Chem. Soc., Washington, DC 1961). (44) R. W. Taft, M. H. Abraham, R. M. Doherty, and M. J. Kamlet, The molecular properties gov- erning solubilities of organic nonelectrolytes in water. Nature, 313, January 31, 1985. (45) Industrial and Engineering Chemistry 38, p 320 (1946).

j. Soc. Cosmet. Chem., 36, 335-348 (September/October 1985) Mechanical properties of dry, normal, and glycerol-treated skin as measured by the gas-bearing electrodynamometer EUGENE R. COOPER,* PAUL J. MISSEL, DANIEL P. HANNON, and GREGORY B. ALBRIGHT, The Procter & Gamble Company, Miami Valley Laboratories, P.O. Box 39175, Cincinnati, OH 45247. Received March 6, 1985. Synopsis The viscoelastic properties of dry, normal, and glycerol-treated skin of the lower leg have been measured with a gas-bearing electrodynamometer (GBE). Elastic modulus measurements are shown to correlate well with visual assessment of the skin condition by a trained dermatological grader. Dry skin is generally stiffer than normal skin and glycerol treatment can indeed soften the skin. Removal of the outer layers of the stratum corneum by tape stripping resulted in an almost 50% reduction in the moduli--indicating a significant contribution to the mechanical properties of the skin from these layers as measured by the GBE. INTRODUCTION A variety of methods for characterizing tissue mechanical properties have been applied to skin. However, when the objective is to measure the elastic properties of stratum corneum, care must be exercised in the choice of proper instrumentation and the design of appropriate test methodology. Classical stress-strain measurements can be used to characterize strips of isolated stratum corneum under tension (1,2). Most in vivo tensile measurements involve rather large displacements and are certainly influenced heavily by the skin layers to which the stratum corneum is attached (3-5). This is especially true when the stress is applied perpendicular to the skin. Indeed, one major application of such techniques as indentometry and levarometry (6), ballistometry (7), and suction methods (8,9) is the study of age-dependent changes of the dermis (10, 11). More sophisticated experiments measuring the mechanical response of skin as a function of frequency have the advantage that small amplitudes may be used, either perpendicular (12) or parallel (13-15) to the skin surface. These techniques show promise in being easy to use and possibly able to separate dermal and epidermal response components at different frequencies (14), with a little interpretation. The two techniques which probably provide the most direct information regarding stratum corneum mechanical properties are the low-torque torsional method of Rigal and Leveque (16) and the gas-bearing electrodynamometer (GBE) of Christensen eta/. (17,18). We have used a dynamometer identical to that of Christensen eta/. in our studies. The GBE measures the displacement of skin in response to a sinusoidal driving force. The force coil and displacement measurement core are mounted on the same * Present Address: Alcon Laboratories, 6201 South Freeway, Fort Worth, TX 76134. 335