J. Cosmet. Sci., 56, 65-77 CTanuary/February 2005) Electron spectroscopy and microscopy applied to chemical and structural analysis of hair B. C. BEARD, A. JOHNSON, F. M. CAMBRIA, and P. N. TRINH, Akzo Nobel Surfactants America, Akzo Nobel Chemicals, 1 Livingstone Ave., Dobbs Ferry, NY 10522. Synopsis The application of surface specific x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) will be shown to be an effective means for the elucidation of hair fiber surface chemistry and structure. Example studies of bleaching and fiber conditioning treatments are discussed. The bleached fiber surface is found to become more hydrophilic due to the loss of the naturally occurring hydrocarbon overlayer and oxidation of surface functional groups as a result of bleaching. Comparison between generic bleaching regimens illustrates the importance of increased pH and the presence of surfactant for effective treatment. Adsorption of conditioning diester quat and dimethicone molecules reintroduces a hydrophobic like surface layer on the hair fiber. Spectroscopic data indicates a segregated adsorption structure of the chemically different conditioning molecules. Electron microscope Images of the conditioned hair shows a smooth uniform surface. INTRODUCTION Human hair is a complex and variable material, composed of an inner spindle overlaid with 5-10 layers of cuticle arranged like roofing shingles. Comprised of proteins, hair contains C, 0, N and S in proportion to the amino acids present. The terminal hair surface, therefore is a mix of all the possible organic functionalities present in the amino acids, (carboxylate, sulfonate, hydroxyl, amine, disulfide, thio ether, aromatic, alkyl, etc.). Cross links at the exterior, cuticle portion of the hair fiber, are substantially more numerous than in the whole hair due to the concentration of sulfur containing cystine amino acid. Upon aging or chemical treatment of the hair, some of the disulfide cross links of cystine are oxidized, resulting in the formation of sulfonate groups at the surface (1). The carboxylate and sulfonate groups play a primary role in surface treatment interactions owing to their charge at near neutral pH. The isoelectric point for hair has been found to be around 3.7 (2). Through an oversight, this paper was omitted from "Proceedings of the First International Conference on Applied Hair Science, Princeton, New Jersey,June 9-10, 2004," sponsored by TRI/Princeton and published by the journal of Cosmetic Science in a 2004 supplement to Volume 55. As with the other papers in the supplement, this paper has been only minimally edited (for conformity to journal format) by the Society of Cosmetic Chemists. * Address all correspondence to B. C. Beard. 65

66 JOURNAL OF COSMETIC SCIENCE Surface analysis of mammal fibers by electron spectroscopy dates back to at least 1972, where Millard studied oxidative surface treatments of wool (3 ). In this early application of XPS, Millard demonstrated the ability to resolve multiple chemical states of sulfur on the surface of the hair fiber. In this technique, electrons ejected by x-ray photon exci­ tation are collected and energy analyzed to provide quantitative elemental and chemical state data. The kinetic energy of the detected photoelectrons reflects the core electron binding energy, (binding energy = x-ray energy - measured electron kinetic energy), which is specific for the emitting element and it's chemical state. Since the kinetic energy of the photoelectrons is limited to the x-ray energy (typically either characteristic Mg ka = 1254.6 eV or Al ka = 1486.7 eV) the transport length through the sample prior to suffering an inelastic collision (inelastic mean free path) is short, 1-3 nm. As a consequence, the electrons finding their way out of the sample and to the detector with energies characteristic of the emitting atom, emerge from no greater than -10 nm into the sample. Overlayers on a sample surface therefore readily attenuate the substrate signal. The XPS technique is capable of observing every element with the exception of H and He. In the Results and Discussion sections of this paper molecular formula will be expressed in terms of C, 0, N, and S. Compositions will be expressed on a 100% basis considering only C, 0, N, and S. In this paper we wish to discuss the chemical modification of the hair fiber surface by the action of hydrogen peroxide based bleaching solutions and the formation of over­ layers as a result of treatment with conditioning formulations. Discussion of the inter­ action between quaternary ammonium based surfactants and the hair surface studied by XPS has been published by the author recently (4). EXPERIMENT AL TREATMENT PROCEDURE European Brown Hair samples for this investigation were obtained from International Hair Importers & Products, Inc., Valhalla, NY. The hair was dipped into a 10 wt% sodium ether sulfate solution and washed by rubbing between the fingers for 1 minute. After washing the hair was thoroughly rinsed with warm distilled water. A portion of the washed hair tress was cut free and set aside to dry for the blank, the other portion would be further treated. The bleaching treatment employed three differing solutions. 1. A 3% hydrogen peroxide solution 2. A 3% hydrogen peroxide solution plus a sodium bisulfile activator at pH = 9. 3. A 3% hydrogen peroxide solution, sodium bisulfite activator, and 0.25% sodium lauryl sulfate, at pH = 9 The three treatments were applied to hair samples for either 30 or 45 minutes, rinsed, and then dried. CONDITIONING TREATMENT FORMULATION The test conditioning formulation prepared for this study is given in Table I. The conditioner was exposed to hair swatches which were previously bleached for 45 minutes