EFFECTS OF SURFACTANTS ON HAIR FRICTION 183 SIDE VIEW SCALEi (a) (b) Figure 1. '(a) Photograph of Apparatus. (b) Schematic of Apparatus. 1-Crosshead, 2-Support blocks, 3-Hanger plate, 4-Screw Assembly for positioning hanger plate, 5-Motor, 6-Hinged platform for tensioning belt, 7-Geared pulleys, 8-Drive belt, 9-Flanged bearings, 10-Geared couplings, 11-Mandrels, 12-Sleeve couplings, 13-Set-screw collars. Table I Effect of Load T• (grams) 0.46 0.85 1.40 2.20 F.C. 0.26 0.25 0.23 0.23

184 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS WRAP ANGLE The test equipment allows choice among three angles, depending on frictional forces anticipated. A large angle (348 ø) is generally suitable for dry friction of hair on any type of mandrel and the smaller angles (97 ø, 210 ø) for wet friction. The effect of wrap angle for hair fibers in dilute cationic solution is shown in Table II. Table II Effect of Wrap Angle Wrap Angle 97 ø 210 ø 348 ø T2/T • 1.37 1.74 2.47 F.C. 0.19 0.15 0.15 Higher friction at 97 ø may be caused by wet fiber compression on the mandrels which increases the wrap angle over that geometrically calculated. This effect should be less important at larger angles. In any case frictional effects should be compared on a common substrate using the same wrap angle. RUB SUBSTRATE Mandrels of • in diameter are used routinely since other sizes affect wrap angle and peripheral speed. Mandrels of several compositions are compared in Table III using bleached fibers and commercial products diluted to 0.1% active ingredient (AI). Table III Mandrel Composition Frictional Coefficients 0.1% AI Dilutions Teflon Wool Fabric Hard Rubber Lucite Comm. TEALS Shampoo 0.07 0.34 0.43 0.44 Comm. Creme Rinse 0.06 0.19 0.29 0.31 Hard rubber, a common comb material, is principally used as substrate because high friction values tend to exaggerate treatment differences. Schwartz and Knowles (24) compared seven substrates and found that lucite and hard rubber give high wet friction exceeded only by glass. FIBER DIAMETER In several experiments, fiber diameter showed no relation to friction. Ten fine and 10 coarse fibers gave almost identical average results for wet friction. Since area of contact is a function of total surface area and hence diameter, friction of fibers appears independent of contact area as Amonton's law predicts. Frishman, et al., (29) also found no relation between the frictional coefficient and fiber diameter among 49 fibers. Others (30) however report correlation. Evidence, such as frictional increase by fiber swelling (22) and decrease by roughening the mandrels (22, 25) has led to general acceptance that contact area does influence friction and that Amonton's equation