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.

186 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Electro microbalance Liquid •- (•.•..s Fiber pecimen -- •Elevator (fine) '•,,Elevator (coarse) Comp Control unit Figure 2. Illustration of the apparatus for wetting force measurement. Two types of wetting force were evaluated on a hair fiber while the liquid level was moved along the fiber at a constant rate (1.1 mm/min). One was taken at liquid advancement, "advancing wetting force," distinguished by subscript "a," and the other at "receding wetting force," distinguished by subscript "r." Perimeter determination. The perimeter of a sample fiber was determined microscopically and calculated from cross sections of mongoloid hair fibers that are generally elliptical in shape. The lengths of the major and the minor axes were determined, and then the perimeters were calculated. Table I Water Transport Results Along Variously Treated Human Hair Fibers a Number of fibers 10 5 3 2 1 Untreated X X X X X Chlorinated DCCA 3% b O O /• /• X DCCA 6% b O O O /% X DCCA 10% b O O O /• X Rubbed c O O O /X X a Symbols denote that (¸): water transport occurred (X): water transport did not occur and (A): water transport sometimes occurred. b Hair fibers were treated with this % of DCCA (dichloroisocyanuric acid) solution. c Hair fibers were treated by rubbing against CC-1500 sandpaper.