ESCA OF POLYMERS ON HAIR 241 DISULFIDE ROOT E N D • 178,5 158.5 BINDING ENERGY (eV) Figure 4. Sulfur high-resolution spectrum of tip-versus-root ends of hair. quaternary nitrogen in high quantities on the tip end. The source of this component is unknown however, it suggests that contamination by quaternary ammonium-con- taining material is the source of the scatter observed in the data for this particular sample. (Note that a small quantity of NR4 + was also observed on the tip half of sample A). Occasional contamination is not surprising in view of the source and nature of the substrate. POLYMER-TREATED SAMPLES Polymer deposition is again readily detected. However, examination of the Polyquater- nium-10 data reveals very interesting substantivity behavior. The surface composition data (Table VI) reveal generally higher oxygen and lower nitrogen contents on the tip end samples (except for specimen C). These observations suggest preferential polymer adsorption at the tip ends. This conclusion is confirmed upon inspection of the high- resolution data which in all cases show higher levels of cellulosic type carbon (C- O type) and greater amounts of quaternary nitrogen on the tip ends as opposed to the corresponding root ends. This differential adsorption behavior is very interesting. A contribution to the observed behavior is probably the greater availability of ionic attachment sites on the tip end. As previously discussed, the sulfur present on the hair fiber exists in two forms. Of these, the sulfonate type provides anionic sites which are capable of binding the cationic polymer. With increasing thiosulfonate and sulfonate at the tip ends (note S 1/S2 ratio in Table VI), a higher degree of adsorption occurs. Another factor likely to cause an

242 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS increase in adsorption at the tip end is the higher mechanical damage of the hair fibers anticipated in this region. Polyquaternium-24, in contrast, does not exhibit this substantivity behavior. As shown in Table VII, samples treated with this material do not show a clear pattern of prefer- ence for any particular region of the hair fiber. The surface oxygen content in Table VII shows statistically significant differences in the A and D sample pairs however, in one case, the tip half is more oxidized while the other shows the root end to be oxygen-rich. Similarly, none of the four pairs show a statistically significant difference in cellulosic C- O content or NR4 + content. The root and tip end samples show similar degrees of uptake. As previously suggested, this change in the deposition behavior may indicate a reduced dependence on ionic interactions with the substrate to produce adsorption. It is appropriate to assess the relative adsorption of the above cellulose backbone polymers by the cellulosic C- O levels which they confer to the treated hair surfaces. Comparison of the samples treated with Polyquaternium-24 with those exposed to Polyquaternium-10 shows a much greater cellulosic fraction on the hair treated with Polyquaternium-24, regardless of the region examined. This confirms the observations made in the initial set of treatments, which indicate that Polyquaternium-24 was supe- rior in terms of deposition. Evidently, the balance of hydrophobicity and cationic char- acter in Polyquaternium-24 provides a high level of adsorption to the hair substrate. SINGLE FILAMENT ANALYSES The data described thus far was obtained from small bundles of 10-20 individual hair fibers. It was also of interest to use the small spot analysis capability of the ESCA spectrometer used in these experiments to examine individual hair filaments. This was done by suspending single filaments on the sample stage and sequentially analyzing several areas down the length of the fiber. A 300-micron-diameter analysis area was chosen as the best compromise between spatial resolution and analysis time. Two fibers were examined in this fashion for both of the polymer treatments. Figure 5 gives a graphic summary of the data. In this figure, the atomic percent of C- O-type %C-O CARBON 25- 20 15 [] ß ß ß [] [] [] Polyquaternium-24, 1 ß Polyquaternium-24, 2 & Polyquaternlum-10, 1 ß Polyquaternlum-10, 2 ß ß ß I I I I I 2 3 4 5 6 POSITION Figure 5. % C-O carbon versus position along a single-hair filament (analysis area --300 microns in diameter).