190 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 0 200 400 I 600 TIME (sec) Figure 7. Wetting force curve of a chlorinated human hair fiber in water. the increased water transport along DCCA-treated hair fibers is consistent with the increased hydrophilicity of the fiber surfaces. A similar phenomenon was observed in the case of hair fibers rubbed with sandpaper. The results of water transport along physically treated fibers are shown in Table I, and the SEM photograph of this fiber is shown in Figure 5. It can be clearly seen from the photograph that the surface structure is damaged by rubbing with sandpaper. Therefore, there is a strong indication that the change in wicking behavior of rubbed hair is due to the change in the surface properties of the fiber (removal of the surface layer). CONTACT ANGLE An apparatus was constructed according to the Wilhelmy principle (4,5), and the wetting force was measured for individual hair fibers in water. In Figure 6, an example of the experimental results of an untreated hair fiber is shown. This curve was obtained by advancing a liquid (water) for 5 mm, stopping for one minute, and then retreating for 5 mm. The wetting force exerted on the fiber is recorded against time. At point A, the sample fiber contacted water, and from A to B advanced (immersed) in water. Between B and C, the fiber was stationary, from C to D it receded from the water, and at point D the fiber was pulled out of the water. From the A-B region, the advancing contact angle (0 a) is obtained, and the receding contact angle (0 r) is taken from the C-D region. The characteristics of the wetting curve of the untreated hair fiber show that the advancing value is negative, indicating that the hair fiber surface is water- repellent. In addition, the receding value is positive, giving a high hysteresis. Similar results were reported by Penn and Miller (8), Kamath et al. (9), and Hsieh et al. (10) for several fiber/liquid systems having high contact angle values. On the other hand, the advancing wetting force of a chlorinated hair fiber is positive, as shown in Figure 7. In this case, the receding wetting force also increased, and the degree of hysteresis thus decreased. A similar tendency was observed for the physically rubbed hair fiber sample, as shown in Figure 8. However, the advancing wetting force

HAIR DAMAGE 191 Hair-S2 -1 I • • i • • • 0 200 400 600 TIME (sec) Figure 8. Wetting force curve of a physically rubbed human hair fiber in water. of this sample fluctuated highly, showing that the surface damage along the fiber axis was very inhomogeneous after the rubbing treatment. These results, obtained for heavily damaged hair samples, show that the wetting force increases not only upon chemical treatment but also upon physical treatment. We are currently evaluating weakly dam- aged hair fibers. In Table III, the advancing and receding contact angle data of untreated and damaged hair fibers are summarized. Averaged values of 0 for hair fiber samples decrease upon chlorination, and also correlate with the degree of chlorination however, the fluctuation in data among the samples is very high, as shown by the standard deviation values. These results strongly support the validity of our method using an electrical capacitance technique. The results shown here are consistent with the prediction by the equation of Washburn (11), which shows that the rate of water transport is influenced by the advancing contact angle values, if the radius of the capillary is constant. Table III Advancing and Receding Wettabilities of Variously Treated Human Hair Fibers a Advancing Receding Sample cos 0 a 0 a (deg) cos O• O• (deg) Untreated -0.21 102 -+ 5.4 0.57 55 +- 3.6 Chlorinated DCCA 3% b 0.37 68 +- 15.3 0.97 12 +- 12.0 DCCA 6% b 0.57 54 +- 10.9 0.95 11 -+ 10.3 DCCA 10% • 0.66 48 +- 9.7 1.13 0 Rubbed c 0.08 85 +- 10.3 0.95 18 + 10.1 a Each value is averaged for 15 fiber samples, and the standard deviation values are also shown for 0• and 0•. u Dichloroisocyanuric acid. c Rubbed against CC-1500 sandpaper.