38 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS w w ! w z Rz Figure 13. Mean values of roughness parameters of 20 hair fibers before and after shampoo treatment scanned at different distances from the root (scan length 0.40 mm). TRANSVERSE MEASUREMENTS Several difficulties had to be overcome before reliable data could be obtained: a) stretching and bending of the hair fiber during stylus contact can be recognized by systematically skewed signals this could be avoided by using the instrument illus- trated in Figure 3 Po Figure 14. Mean values of actual profile length and peak count of 20 hair fibers before and after shampoo treatment scanned at different distances from the root (scan length 0.40 mm).

PROFILOMETRY OF HAIR 39 b) falsification of the contour of the fiber caused by inertness of the stylus, if the scan speed is too high c) insufficiently fixed hair-fibers. Figure 15 shows the almost symmetrical signal of a fiber, after the above mentioned problems were solved (6). The influence of pH on the swelling behavior of hair is well known (9). Alkaline pH values increase the fiber diameter considerably more than slightly acidic pH (Figure 16). In this experiment the fiber had been covered with a drop of the respective buffer and scanned repeatedly (6). Determination of fiber ellipticity and orientation of short segments of hair fibers. An elliptical long hair will lie on the slide surface with an undefined angle, and the dimensions of the two axes are unknown. A computer algorithm has been developed to determine the three parameters from the contour of the scans. Figure 17 reflects some examples of ellipses fitting best into the contour of scan, with the longer of the axes parallel to the support (a) and with optimal fitting and free orientation of the axes (b). Figures 18a, b shows the longitudinal surface profile of a fiber before and after twisting around its axis. While the vertical scale in the upper profile extends over about 14 •m, the scale of the lower half is extended over about 27 •m. The difference between the two profiles of the same fiber is that in the upper half the long ellipsoidal axes will probably lie parallel to the support, while in the lower half the fiber winds like a helix. This means that the ellipses stand vertical to the support every 8 mm, causing regular valleys and mountains. The differences between the ellipsoidal axes can be measured. Using additional transverse measurements, both a and b can be measured. o L rv' G.. I. fl Z lOO Z / // '-' I / // [ I / : // I / "// ø I s B Figure 15. Changes of hair surface roughness after treatment with shampoo (every other day).