352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS HsC • (•)• C 2H 5 2j N • O• HsC2 Calls O COOH Rhodamine B Figure 1. Structure ooe Rhodamine B. produced a significant increase in scale penetration and scale face deposition. This is much more pronounced after four hours of bleaching (Figure 2c), where the scale face appears to be extensively marked by the tracer. In the 30 minute bleach creme treat- ment, the scale faces show slightly less fluorescence intensity (FI) than in the four hour peroxide treatment. In order to quantify this behavior, longitudinal scans of fluorescence intensity were made along 2.2 mm of fiber surface, as seen in Figure 3. Fluorescence intensity levels were quite uniform in all samples. The outlining of scale edges in the untreated and the one hour hydrogen peroxide treated, and the extensive scale penetration, as shown for the four hour treated fiber, are clearly noticeable. In Figure 4, average values of fluorescence intensity show a considerable increase as a result of oxidative damage. In general, the fluorescence intensity increased with increas- ing peroxide treatment times, and a major level of oxidative surface damage occurred already within one hour. The 30 minute bleach creme treatment produced essentially the same level of oxidative surface damage as the four hour 6% H202 treatment. Scanning electron microscopy. When viewed by SEM, untreated and bleached hair showed a variety of features in their surface topography, as seen in Figure 5. Besides the normal cuticles of untreated fibers, loose and broken-off cuticle edges were observed. Fibers of all four categories displayed cuticles with holes in them, although hole formation was most extensive in bleached hair. Erosion of the cuticle face was observed after the four hour bleach treatment prior to subsequent combing. The bleach creme treatment produced the least topographical damage among the bleaching conditions we investi- gated. Wettability. The surface of intact untreated hair is dominated by the hydrophobic epicuticle, while bleaching produces a hydrophilic hair fiber surface. Figure 6 illustrates the factors involved in solid-liquid interactions. A hydrophilic fiber (a) shows a low contact angle (0) with a hydrophilic liquid such as water, which has a surface tension CrLV of --72 mN/m. This results in a concave meniscus at the fiber-liquid contact line and a positive wetting force, F w. A hydrophobic fiber (b), such as the root end of an untreated hair fiber, forms an obtuse contact angle with water, resulting in a convex meniscus and a corresponding negative wetting force.

EVALUATION OF HAIR DAMAGE 353