INTERFIBER ADHESION 3 5 9 FORCE {p. ,N) IO- UNTR. 0 -I0 -20 N UJOL Figure 9. Adhesion force curves for human hair fibers treated with Nujol. FORCE {u.N) 20:- iO UNTR. 0 -I0 -20 VASELINE HAIR TONIC --• FIBER POSITION Figure 10. Adhesion force curves for human hair fibers treated with Vaseline hair tonic. Variations in the adhesion forces are smaller than those observed in the case of Polymer JR-400-treated fibers. Since synthetic sebum is an oily material, the mechanism of adhesion seems to be guided by the surface tension of the liquid. There does not seem to be a consistent effect of concentration. This may be due to insignificant variations in add-on, although it should be noted that in treatments of hair swatches significant differences in add-on were obtained by changing the concentration of the treating liquid. However, in the treatment of fiber assemblies, solution is held between fibers by cap- illary forces, an effect that is not possible on single fibers. PART II: DYNAMIC PULL-OUT FORCE MEASUREMENT Although the method of measuring adhesion forces during static point contact between two fibers, which is described above, works satisfactorily when the surface films are continuous and the forces acting between the fibers at the point of contact are capillary forces, it was shown to be inadequate in our efforts to establish correlations between adhesion and compressibility parameters (3). Because of the parallel alignment of the fibers in a hair swatch, the forces of interfiber adhesion could be quite high, since a large number of contact points are involved. We have therefore developed a method to

360 JOURNAL OF COSMETIC SCIENCE Table IV Adhesion Forces Between Pairs of Nylon-6 and Human Hair Fiber Treated With Various Liquids Liquid surface tension Treatment (pN/m) Force (pN) Nylon-6 Human hair Observed Calculated Untreated 2.8 + 0.7 0.1 + 0.1 Nujol 35 7.0 + 0.3 6.3 6.6 + 0.3 Untreated 2.8 + 0.6 -- Glycerol 64 6.4 + 0.6 11.5 -- Untreated 1.6 + 0.8 0 Vaseline hair tonic 31 5.6 + 0.2 5.6 13.9 + 0.7 8.1 _+0.2 Based on contact perimeter of 180 pm. All entries are averages of 20 measurements at 95% confidence level. Table V Adhesion Forces Between Pairs of Human Hair Fibers Treated With Synthetic Sebum Adhesion force (pN) SSB concentration (%) Pair 1 Pair 2 0 0 0 0.5 7.2 + 0.9 10.0 + 1.7 0 1.1 + 0.6 0.4 + 0.4 1.0 2.2 + 0.7 4.7 + 1.2 0 0 0 1.5 5.2 + 0.8 7.0 + 0.9 All entries are averages of 20 measurements at 95% confidence level. measure the force of adhesion acting on a fiber resulting from its longitudinal contact with other parallel fibers in an assembly. Although this method is not as controlled as the single-point contact method, the results seem to correlate better with the assembly behavior. It should be noted that the concept for this method is not new. Denby and Andrews (4) measured forces of withdrawal of single fibers from wool fabrics to interpret felting behavior. EXPERIMENTAL The apparatus used for the measurement of "dynamic" interfiber adhesion is shown in Figure 11a. The hair assembly is packed into an aluminum cylinder (40-mm long, 15-mm diameter), with a single hair partly pulled out and attached to a hook with Duco © cement as shown in Figure 1 lb. Direct attachment of the fiber to the hook of a Cahn recording electrobalance gives rise to a noisy zero line when the system is at rest. It appears that small vibrations are directly transmitted to the balance beam by the single hair, but interposing a fine Kevlar © monofilament between hair and hook elimi-