332 JOURNAL OF COSMETIC SCIENCE where L = length, M = moment of inertia for the pendulum mass, T = period, a = semi major axis, and b = semi minor axis. The semi axes of the elliptical fiber cross section, were determined with a laser mi- crometer by rotating the fiber on its axis in the laser beam. RESULTS EFFECT OF CUTICLE REMOV Al Figure 3 shows the results of an experiment in which the shear modulus of hair fibers was measured before and after abrasive removal of the cuticle layer. The shear modulus of untreated (i.e., control) hair fibers was measured and found to be approximately 1.0 GPa. The same specimens were abraded to remove the cuticle layer (i.e., decuticled) and measured again. The shear modulus of the decuticled fibers was on average approxi- mately 0.6 GPa which is 40% less than that of the fibers before they were abraded. The two non-overlapping significance circles (right side of the graph) and the comparison table (below the graph) show that this difference is highly significant. These results clearly show the major influence of the cuticle layer on the shear modulus of hair fibers. EFFECT OF TREATMENTS ON SHEAR MODULUS-EXPANDED STUDIES Bleaching+ cetyl trimethylammonium bromide (CETAB). Figure 4 shows the results for the ... -•-- ~_,, .,..__HH .,._,,,., ., .. ,, . ., .. ., . ., ··--- , .. ' .. ·-·- ., , ., , .. ,.,,.,,. Onaway Analysis of Shear Modulus By Treatment 1.2 1.1- •· 1- -.1 ... 1/) .. ::I . • =i .. _h -g 0.9- ., :::i! =-- ii a.a- . - .c t. •• v, 0.7- . I t 0.6- ... "' 0.5 I I Untreated Bleached CETAB ····-•"'. .. , . 0 0 0 All Pairs . . Tu key-Kramer i Means Comparisons !---:· ·- . Treatment 0.05 -- " [ Comparisons for all pairs using Tukey-Kramer HSD Level Mean Untreated A 1.0404402 CETAB B 0.8843395 Bleached C 0.6253302 Levels not connected by same letter are significantly different. ... , --•' Figure 4. Effect of bleaching and subsequent CET AB treatment on shear modulus.

2006 TRI/PRINCETON CONFERENCE 333 effects of bleaching and the effects of subsequent cetyl trimethylammonium bromide treatment. Initially, the shear modulus of untreated hair fibers was measured and found to be in the range of 1 to 1.1 GPa. The same specimens were bleached (commercial product, 90 min.) and measured again. The shear modulus dropped to 0.6 to 0.7 GPa which is a 40% reduction indicating that the cuticle layer and the cortex was softened by the bleaching process. Subsequent treatment with CETAB (0.5%, 30 min., rinsed) resulted in the shear moduli increasing to 0.8 to 1.0 GPa which is midway between that of the Untreated and the Bleached fibers. The non-overlapping significance circles and the comparison table show that these differences are highly significant. The bleaching process oxidizes cystine by breaking disulfide bonds and creates cysteic acid groups both in the cuticle and the cortex. Breaking the disulfide bonds lowers the shear modulus of the fiber. However, it is important to note that the shear modulus of the fiber is dominated by the cortex because it contributes more to the volume of the fiber. The greater effect of CETAB in restoring the shear modulus comes from its ability to penetrate into the cortex of hair. This has been shown independently by mass spectroscopy methods (4). The penetrated CETAB molecules form salt linkages and hydrophobic bonds which act as secondary valence cross-links, thus fortifying the in- ternal structure of the endocuticular proteins in the cuticle and the keratin associated proteins in the cortex as shown in Figure 5. Bleaching + Polyquaternium-10 (PQ-10). Figure 6 shows the results for the effects of bleaching (commercial product, 90 min.) and the effects of subsequent polyquaternium- 10 (PQ-10) treatment (0.5%, 30 min., rinsed). The experimental design of this study was the same as the CETAB study. The shear moduli of the untreated (1 to 1.1 GPa) and bleached fibers (approximately 0.7 GPa) are similar to the CETAB study. The effect of subsequent treatment with PQ-10 is much different----0nly a slight increase in shear modulus to approximately 0.8 GPa. Other studies have shown that polyquaternium-10 INTERCELLULAR DIFFUSION .,. TRANSCELLULAR DIFFUSION �::::, ��-�/.'••:-...:. .❖:•: • • · • ••• .. •• , ......·• �7:,•: cu,I �- - ::� --...INTEIINCIIIFllllllllAII �- Figure 5. Possible mechanism of fortification via hydrophobic bonding.