280 JOURNAL OF COSMETIC SCIENCE (a) co) (½) Figure 3. a: Untreated virgin bleached hair. b: Virgin bleached hair exposed to aqueous environment at pH 9.5 and 29.9øC. Some raising of the cuticle is visible. c: Hair treated with 3% Merquat-100 at pH 7. Conditioning treatment is expected to smooth and lower the cuticle in damaged hair. was treated only once with the polymer solution to allow fair comparison to the other techniques. However, the many images obtained from both untreated and treat- ed hair showed less roughening on the conditioned cuticle compared to the untreated. While ESEM is useful for revealing surface topography of the hair, it was not useful for determining the distribution of Merquat over the surface owing to lack of topo- graphic or Z contrast (except at unreasonably high polymer doses). Hair treated with N-Merquat and P-Merquat was examined using EDS. The elemental composi- tion of N-Merquat was not sufficiently different from that of the hair to allow EDS mapping of the polymer distribution. In principle, the theoretical level of P in the P-Merquat ought to be high enough to allow detection by EDS. However, in practice, the concentration of P over the surface of P-Merquat-treated hair was below the detec- tion limit, and this approach was abandoned in favour of SIMS and XPS. Beam damage can be a problem in ESEM, especially with hydrated biological materials during EDS (14). In this study, beam damage to the hair did not appear to occur under normal operating conditions. XPS The XPS spectrum of untreated hair is given in Figure 4. This shows the presence of carbon, nitrogen, oxygen, sulphur, and silicon from the outer surface of the epicuticle. The first four elements were expected, as they form the biological matrix of the hair, the epicuticle being rich in the amino acid cysteine, which contains keratinized disulfide bonds that give the hair its strength (1). Silicon on the surface of hair can be explained by the presence of silicon polymers in many shampoo and conditioner formulations (20), and the hair may have been treated with these prior to study. In addition, it is commonly known that silicones contaminate the surface of most materials, in particular polymers (21), which makes any surface study of silicon difficult. Peak fitting was carried out on regional elemental spectra to obtain information on the chemical environment. The carbon Is photoelectron spectra was resolved to two peaks, with the most intense due to both the hydrocarbon chains present in the protein and pump oil contamination. The less intense peak was due to the carbon from the carboxylic groups in the protein matrix. The nitrogen and oxygen Is peaks at 399.9 eV and 531.8 eV, respectively, were char- acteristic of the organic biological matrix formed from the amino acids (22). For the

ADSORPTION OF POLYMER ONTO HAIR 281 5000- ß • 4000 • 3000 Cls 2000 Ols 1000 • S2p Si2p 1000 900 800 700 600 500 400 300 200 100 0 Binding Energy/eV Figure 4. Wide-scan XPS spectra of bleached hair. silicon 2p peak, regional spectra showed a singlet at 101.9 eV, confirming the presence of silicones or silanes on the surface of the hair (22). Analysis of the spectra from the N-Merquat©-100 and P-Merquat©-100-treated hair showed no new peaks compared to the untreated. It appeared that XPS was not sensitive enough to detect any additional phosphorus or chlorine that would be present due to polymer adsorption. A more sensitive technique is therefore needed to detect any ad- sorbed polymer, and whereas the sensitivity for XPS is around 1000 ppm, SIMS enables the detection of most elements down to the 1-10 ppm scale. SECONDARY ION MASS SPECTROMETRY (SIMS) SIMS spectra of hair lengths: Untreated hair. A negative SIMS spectrum of an untreated hair's outer surface is given in Figure 5a. The instrument was configured so that only ions sputtered from the hair were detected. The acquisition time for spectra was approxi- mately two minutes, and this sputtered less than 10% of the thickness of the epicuticle. In agreement with the XPS measurements, C- (12D), CH- (13D), O- (16D) OH- (17D), C 2- (24D), C2H- (25D), CN- (26D) and S- (32D) peaks were observed, these making up the biological matrix at the surface. Of particular interest in the spectrum are the peaks at 19 D (F-) and 35/37 D (Cl-), which were undetected using XPS. These are therefore present in small amounts at the surface ( 1000 ppm) however, it should be noted that the relative intensities of the peaks for the different species in SIMS cannot be compared directly, as the sensitivity factors of the elements vary greatly. It is thought that the chlorine may originate from the bleaching process. An explanation for the presence of fluorine is that the hair may have been treated prior to study with a cosmetic containing a fluorocarbon surfactant or polymer, which are used due to their very low surface free energies. A positive ion spectrum was also acquired, although, apart from sodium (23D), potassium (39D) and silicon (28D) peaks, there was nothing further of interest. Traces of sodium and potassium were detected due to their very high sensitivity in SIMS and are present as trace metals in the hair. SIMS spectra of hair lengths: P- and N-Merquat©-lOO-treated hair. The negative SIMS spectrum of hair treated with N-Merquat©-100 is given in Figure 5b. This spectrum is