354 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS FI(% 100- 20' (a) Unbleached 0.4 0.9 1 '3 118 212 DISTANCE ( mm ) FI(%) 1 2O 0 0.0 0.4 0.9 1.3 1.8 2.2 DISTANCE (mm ) FI(%) 100' (C) 6% H202, 4 h FI(%) 100 t 40' 20' (d) Bleach creme, 30 min o o.o 0.4 0.9 1.3 1.8 2,2 o. 0.4 0.9 1,3 1.8 2,2 DISTANCE (mm ) DISTANCE (mm ) Figure 3. Longitudinal fluorescence intensity scans of unbleached and bleached hair fibers treated with Rhodamine B. The wetting force is given by equation 1: F w = PCrzv COS0 a (1) where P is the fiber perimeter, Crzv the liquid surface tension, and 0a the advancing contact angle. The fiber perimeter is measured with hexadecane in a separate experi- ment, and the liquid surface tension is measured with a platinum wire. Work of adhesion, W, used in this work as an index of surface energy, is defined in the present context as the work required to separate a solid/liquid system at the interface: W = Crzv (1 + COS0a) (2) Figure 7 shows the effects of various oxidative treatments on the wettability of hair fibers. The repeated short time treatment in 6% H202 (2' X 10) and the bleach creme treatment are similar in their effects on water wettability, approaching surface energy levels close to that of the one hour treatment in 6% H202. The two minute bleach treatment repeated ten times has a total bleaching time of 20 minutes. Since the bleaching solution is most effective at the start of the bleaching treatment, and a fresh solution was used at each of the ten treatments, it seems reasonable that this sample would show greater change than one subjected to a single 30 minute bleach treatment. The bleach creme treated sample had a W value in agreement with other 9% H202

EVALUATION OF HAIR DAMAGE 355 FI (%) lOO 8O 6O 4O 2O Untr I h 4h Treatment Bleach creme Figure 4. Average fluorescence intensity for five each of longitudinally scanned unbleached and bleached fibers treated with Rhodamine B. treatments done in our labs under similar conditions. Although the surface of the hair shows a relatively low level of wettability, we have seen that damage to the fiber interior is more extensive than one might expect from the observed change in surface properties. We also studied the water wettability of unbleached and bleached hair permed one, two, and three times. In contrast to the increased wettability of bleached hair, after bleaching even repeated perm treatments did not produce a major increase in wettability. This observation was somewhat surprising since reductive scission of disulfide bonds leads to the formation of two hydrophilic sulfydryl groups that would be expected to produce an increase in the hydrophilicity of the hair fiber surface. In previous (8) studies of the effect of reduction without subsequent reoxidation (neutralization) on the wettability of hair, we observed that wettability increased rapidly and leveled off at W values of 85-90 mN/m. This difference from the previously observed behavior must be attributed to the fact that the neutralization step (3% H202) following the perming apparently leads to extensive reformation of the original disulfide bonds in the surface regions of the hair. Although bond reformation with peroxide is known not to be complete, the surface sulfydryl groups are the most accessible to reformation and would be the first and most easily affected. Structural changes Dye diffusion. The rate of dye transport in keratin fibers is strongly affected by the nature of the fiber structure. Any decrease in the disulfide crosslink density in the matrix and