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The complex chemical structure of the hair surface is far from being completely understood. Current understanding is based on Rivett's model1 that was proposed to explain the macroscopic hydrophobic nature of the surface of natural hair. In this model covalently-linked fatty acids are chemically grafted to the amorphous protein (keratin) through a thio-ester linkage2,3. Nevertheless, experience like wetting and electrical properties of human hair surface4 shows that the complexity of the hair surface understood be fully understand based on this model.
Recent studies in our laboratory show for the first time microscopic evidence of the heterogeneous physico-chemical character of the hair surface. By using Chemical Force Microscopy, the presence of hydrophobic and ionic species are detected and localized, before and after a cosmetic treatment (bleaching). Based on force curve analysis the mapping of the local distribution of hydrophilic and hydrophobic groups of hair surface is obtained. A discussion on a more plausible hair model and its implications will be presented based on these new results.
References
1.A.P. Negri, H.J. Cornell, D.E. Rivett, Textile Res. J.. 63, 1997, 199.
2.Swift, J.A Humain hair cuticule: Biologically conspired to the owner's advantage, J. Cosmet. Sci. 1999, 50 (1), 23-47.
3.S. Breakspear, J. R. Smith, G. Luengo, J. of Structural Biology 149, 2005, 235.
4. V. Dupres, D. Langevin, P. Guenouun, A. Checco, G. Luengo, F. Leroy. J. Of Colloid and Interface Science 306, 2007, 34.
5.C.R. Robbins in Chemical and Physical behavior of human hair 4th edition.ed.Springer.
6.Yorimoto, N., Naito, S. Physical and Chemical properties of integral lipids in hair cell membrane complex, Inc Proc. Int. Symp. Fibre Sci. Technol, Yokohama, 1994, 215.
7.Aleksander Noy, D. V. Veznov and Charles M. Lieber : Chemical Force Microscopy, Annu. Rev. Mater. 1997, 27, 381-421.
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