N(E) Min: 23 Max: 55059 0(1s) 602 541,8 481,6 HAIR SURFACE CHEMISTRY C(1s) \ S(2s) S(2p) ��-�------�,� 69 421.4 361.2 301 240,8 180.6 120.4 60.2 -4.57764e-005 Binding Energy (eV) Figure 1. Survey scan of a blank hair sample. By tracking surface C content versus bleaching treatment solution and time, an indi­ cation of efficacy can be achieved. Figure 4 illustrates that the change in surface chem­ istry is most dramatic when the bleaching solution is at pH = 9 and surfactant is present. The hydrogen peroxide solution alone is relatively ineffective even over the 45 minute exposure period studied. Clearly the increased pH is an important factor and the small (0.25%) addition of surfactant has a measurable effect in addition. The chemical state information available from the high resolution XPS data clarifies the mechanism associated with this change in surface composition. Figure 5 is an overlay of the C(ls) high resolution spectra from the blank and bleached hair samples referred to in Table II. The blank hair spectrum is dominated by a single chemical state peak indicative of hydrocarbon (saturated, C-C/C-H bonding) at the outer most surface. After bleaching however, the surface has a much greater contribution from carbon associated with more electronegative elements (C-N/C-O bonding) which are present in the hair chemistry. This information leads to the conclusion that the bleaching removes a hy­ drocarbon overlayer revealing the hair structure itself. The removal of the hydrophobic hydrocarbon overlayer permits access of the water borne peroxide to the hair surface. Surfactancy imparted by the small addition of sodium lauryl sulfate allows more inti­ mate wetting of the surface and solvation of the hydrocarbon layer away from the hair fiber. The oxidative effect of hydrogen peroxide causes a measurable increase in the oxidized sulfur groups at the hair surface. Figure 6 shows the amount of oxidized sulfur groups at the surface resulting from the various bleaching treatments. The hydrogen peroxide solution alone had no effect, consistent with the very limited reduction in surface hydrocarbon overlayer content. The peroxide at elevated pH did oxidize the surface, however, after an induction time, where presumably the hydrocarbon overlayer

70 JOURNAL OF COSMETIC SCIENCE Photo No. :: 24 Time :8:46:32 Figure 2. SEM image of untreated (blank) hair fibers. Cuticle structure is rough and subdued. was degraded due to the alkalinity of the solution. Addition of surfactant on the other hand allowed for the rapid reaction of peroxide with the surface of the hair fiber. The apparent induction time to activity noted in the pH = 9 bleaching treatment is absent or greatly minimized through the inclusion of modest amounts of surfactant in the bleach­ ing formulation. This accelerated activity is attributed to the beneficial effect of surfac­ tancy in removing the hydrocarbon overlayer. The attenuation of the characteristic N & S signals from the hair matrix can be used as a means for estimating the hydrocarbon layer thickness on the hair surface. A number of assumptions need to be made in order to carry out the calculation of overlayer thickness: 1. The substrate surface composition (hair) is taken to be represented by the bulk elemental composition using the relative abundance of the various amino acids present in the hair. The bulk elemental composition in units of atom percent, excluding hy­ drogen is 52.8% C, 30.8% 0, 14.2% N and 2.3% S. 2. The composition of the overlayer is assumed to be far-like with a representative composition of 95% C and 5% 0. 3. The overlayer is assumed to be continuous and uniform. Using these assumptions and tabulated sensitivity factor and inelastic mean free path data (6,7), the calculation finds a layer of approximately 30 Angstroms would yield the observed blank sample surface composition. Microscopic examination of the hair following the 3% hydrogen peroxide, pH = 9, sur-