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J. Cosmet. Sci., 60, 31–44 (January/February 2009) 31 Deposition of 18-MEA onto alkaline-color-treated weathered hair to form a persistent hydrophobicity HIROTO TANAMACHI, SHIGETO INOUE, NORIYUKI TANJI, HISASHI TSUJIMURA, MASASHI OGURI, MIO ISHITA, SHINICHI TOKUNAGA, and FUMIKO SAZANAMI, Beauty Research Center, Kao Corporation, 2-1-3, Bunka, Sumida-ku, Tokyo 131-8501, Japan (H. T., S. T., F. S.) Analytical Science Research Laboratories, Kao Corporation, 1334 Minato, Wakayama-shi, Wakayama, 640-0112, Japan (S. I., N. T.) and Analytical Science Research Laboratories (H. T., M. O.) and Biological Science Research Laboratories (M. I.), Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497, Japan. Accepted for publication September 29, 2008. Synopsis A technology for the deposition of a persistent hydrophobicity to alkaline-color-treated weathered hair sur- faces using 18-MEA (18-methyleicosanoic acid) is presented. Two approaches were examined in order to make 18-MEA bind tightly to the alkaline-color-treated weathered hair surface. One was to apply 18-MEA as an acid form and the other was to apply 18-MEA as a salt or complex. It was found that the combination of 18-MEA with specifi c cationic surfactants [stearoxypropyldimethylamine (SPDA) and docosyldimethyl- amine (DSDA)] makes the alkaline-color-treated weathered hair surface hydrophobic and that its hydropho- bicity is maintained even after shampooing. Characterization of adsorbed layers of 18-MEA/SPDA on a mica surface, as a possible hydrophilic surface model, was performed using atomic force microscopy (AFM) and angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The results revealed that 18-MEA/SPDA formed a layer with high wear resistance, with an alkyl chain, the hydrophobic moiety, oriented at an angle of around 25° to the air interface. INTRODUCTION 18-MEA has been subjected to study for years in hair research science since the dis- covery of its presence on keratinous fi bers (1–3). 18-MEA is thought to be covalently bound, probably via a thioester or ester linkage, to the outer surface of the cuticle (4–7) and is located specifi cally in the cuticle, not in the cortex (6). It is also known that 18-MEA makes the surface hydrophobic and acts as a boundary lubricant to decrease friction resistance (8–11). The precise role of 18-MEA remains unclear, but the large segmental volume of the anteiso-moiety is expected to provide molecular mobility and exhibit liquid-like behavior compared with a straight-chain fatty acid (12,13).