184 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (3). We found that there was a minimum (critical) number of fibers needed for water transport to occur, depending on the wettability of the fiber samples. That is, the water transport behavior of fiber bundles seems to be highly dependent on the apparent hydrophilicity of the fiber surfaces. In this study, we attempted to develop a convenient method for evaluating the degree of damage to hair fibers by observing the water transport behavior along fiber bundles by using an electrical capacitance technique. We compared the results with those of the dynamic wetting forcer measurements on a single hair fiber in water using the Wilhelmy principle (4,5) in order to ascertain the reliability of our method. EXPERIMENTAL SAMPLE MATERIALS Human hair fibers were obtained from a Japanese girl, age 15. All samples were cl•eaned with nonionic detergent solution, and then Soxhlet-extracted successively with a mix- ture of chloroform/methanol (50/50 vol) and diethylether. Surface modification of the human hair fibers was effected by two methods: chlorination with dichloroisocyanuric acid (DCCA) and physical rubbing with sandpaper. Ch[orina- tion was carried out according to the method described by Makinson, who applied it to wool fibers (6). Hair fibers (0.5 g) were immersed in aqueous DCCA solution (50 ml) containing 0.05% of nonionic detergent at pH 6.5 and at 7øC for two minutes. The fibers were then treated with dilute HC1 solution (pH 2.5) for one minute, followed by treatment with 2% sodium hydrosulfite (pH 4.5) for one minute and with 1% sodium bicarbonate at pH 7.5 for one minute, and finally rinsed with deionized water (three times) and dried. Three levels of treatment were applied (3, 6 and 10% DCCA). Physical rubbing was carried out by rubbing a hair fiber against No. CC-1500. sand- paper. Amino acid analyses and scanning electron microscope observations were carried out as described in a previous paper (7). WATER TRANSPORT MEASUREMENT (3) Water transport along a hair fiber bundle was measured using an electrical capacitance technique. A detailed explanation of the apparatus and of the procedure have been given previously (3). The length of the horizontally placed sample hair fiber bundle was 4 cm. CONTACT ANGLE MEASUREMENT The liquid-solid contact angle between water and a single hair fiber was evaluated by measuring the wetting force (F w) according to the Wilhelmy principle (4,5). Wetting force. When a solid is partially immersed in a liquid, the liquid either rises or is depressed along the vertical wall of the solid, thus exerting a force on the solid. The vertical component of this attraction force is the wetting force (Fw), Fw = •tvPcos 0 (1) where y LV is the surface tension of liquid (dyne/cm), P is the perimeter of the solid

HAIR DAMAGE 185 (cm), and 0 is the contact angle between liquid and solid interface. In a setup illustrated in Figure 1, the force detected on a single fiber immersed in a liquid (F) can be assumed as F = F w + Mg - F b (2) where Mg is the weight of fiber and F b is the buoyancy. The weight of the fiber (Mg) can be nulled out before immersion. In addition, buoyancy (F b) of a fine fiber can be neglected since the buoyancy force amounts to only a few thousandths of the wetting force when the fiber diameter is less than 100 •m and the immersion depth is lower than 5 mm. Therefore, the wetting force is the measured force (F): F = F w = •/Lv pcøs 0 (3) Wetting force measurement. For this purpose, an apparatus for wetting force measurement was constructed as shown in Figure 2. It includes a Mettier electrobalance, Model MT5, with a capacity of 5 g and a sensitivity of 1 •g, a Harmonic Drive reversible translator (elevator: Model LA-32) with a Harmonic Drive controller (Model HS-430), and a personal computer (NEC PC-9801FX). The fiber-liquid contact is controlled by moving the wetting liquid up or down by the elevator, which is pulse-driven by the controller through harmonic drive motion according to a computer program. The minimum translational length of the elevator is 0.0174 Ixm/pulse. F Sol id ß sv Vapor Liquid Figure 1. Immersion of a fiber into a liquid.