NANOTRIBOLOGICAL PROPERTIES OF HAIR 55 and end-group effects on the surface tension of poly(dimethylsiloxane), Macromolecules, 26, 3069-3074 (1993). (11) G. Lerebour, S. Cupferman, C. Cohen, and M. N. Bellon-Fontaine, Comparison of surface free energy between reconstructed human epidermis and in situ human skin, Skin Res. Technol., 6, 245-249 (2000). (12) H. Schott, Contact angles and wettability of human skin,]. Pharm. Sci., 60, 1893-1895 (1971). (13) M. E. Ginn, C. M. Noyes, and E. Jungermann, The contact angle of water on viable human skin,]. Colloid Interface Sci., 26, 146-151 (1968). (14) H. Yanazawa, Adhesion model and experimental-verification for polymer SIO2 system, Colloids Surf, 9, 133-145 (1984). (15) B. Bhushan, Principles and Applications of Tribology (Wiley, New York, 1999). (16) B. Bhushan, Introduction to Tribology (Wiley, New York, 2002). (17) B. Bhushan, Handbook of Micro/Nanotribology, 2nd ed. (CRC Press, Boca Raton, Florida, 1999). (18) B. Bhushan (Ed.), Springer Handbook of Nanotechnology (Springer-Verlag, Heidelberg, Germany, 2004). (19) B. Bhushan and C. Dandavate, Thin-film friction and adhesion studies using atomic force microscopy, ]. Appl. Phys., 87, 1201-1210 (2000). APPENDIX A: SHAMPOO AND CONDITIONER TREATMENT PROCEDURE This appendix section outlines the steps involved in washing hair swatches with sham- poo and/or conditioner. SHAMPOO TREATMENTS Shampoo treatments consisted of applying a commercial shampoo evenly down a hair swatch with a syringe. The hair was lathered for 30 seconds, rinsed with tap water for 30 seconds, and the process was repeated. The amount of shampoo used for each hair swatch was 0.1 cc of shampoo per gram of hair. Swatches were hung to dry rn an environmentally controlled laboratory, and then wrapped in aluminum foil. CONDITIONER TREATMENTS A commercial conditioner was applied, 0.1cc of conditioner per gram of hair. The conditioner was applied in a downward direction (scalp to tip) thoroughly throughout the hair swatch for 30 seconds. The swatch was then rinsed thoroughly for 30 seconds. Swatches were hung to dry in an environmentally controlled laboratory, and then wrapped in aluminum foil. APPENDIX B: CONDITIONER THICKNESS APPROXIMATION We consider a cylindrical hair fiber of diameter D = 50 µm (radius R = 25 µm). For conditioner thickness calculations, the following assumptions are made: (a) hair and the material being added have the same density, (b) the coating of material is uniform on the hair surface, (c) the cross-sectional area of a hair fiber remains constant along the longitudinal axis of the fiber (i.e., from root to tip) the hair fiber is perfectly cylindrical (circular cross section), and (d) the deposited conditioner remains bonded to the cuticle surface (no absorption into the cuticle layer). The cross-sectional area of an untreated hair fiber is initially calculated. By adding a

56 JOURNAL OF COSMETIC SCIENCE specified amount of conditioner, this area will increase and cause the radius of the treated hair fiber to increase. This increase in the radius of the treated hair will be equivalent to the thickness of the conditioner layer. The original cross-sectional area A c of hair fiber lS Ac = TIR 2 = 7r(25µm)2 = 1963.4954 µm2 Adding 200 ppm of material to the surface (which is comparable to the amount that commercial conditioners typically deposit) will cause an increase in volume (for a unit fiber length) by 200 ppm, or by 0.0002. Thus, the cross-sectional area Ac,conditioner of the treated hair will increase by the same amount to Ac,conditioner = 1.0002 Ac = 1963.888 µnz2 which results in a new radius Rconditioner' Rconditioner = Ac,conditioner = 25.0025 µm Ti Therefore, subtracting the original radius from the radius after treatment increases the thickness of the hair by 0.0025 microns, or 2.5 nm. It is important to note that the approximation of the conditioner thickness as 2.5 nm was determined for a particular hair diameter and material deposition amount (with the hair and material having equal densities). Although these are generally realistic approxima- tions, hair diameter often varies by a factor of 2 and the deposition level can vary up to an order of magnitude. The conditioner layer has been shown in previous work to be nonuniform as well. Thus, actual conditioner thickness can deviate significantly from this number.