336 JOURNAL OF COSMETIC SCIENCE 30 25 i 20 · � 15 C C 0 10 ·s 5 :!!! 0 -5 Humidity (% RH) Figure 8. Example of hysteresis of moisture sorption-desorption measured gravimetrically. 1.5 1.4 1.3 1.2 � 1.1 0 1 0.9 0.8 0.7 0 10 20 30 40 50 60 70 80 90 100 Humidity (%RH) Figure 9. Effect of moisture sorption-desorption on the shear modulus of untreated hair. found to lower the shear modulus of untreated hair fibers by 40% showing the effect of the cuticle layer in this measurement. Bleaching also lowers the shear modulus of hair by approximately 40% indicating softening of the cuticle layer. Subsequent treatment with CETAB increases the shear modulus of hair indicating fortification of cuticle layer.

2006 TRI/PRINCETON CONFERENCE 337 Figure 10. Original torsion pendulum (left) and next generation torsion pendulum (right). PQ-10, on the other hand, has little effect most likely due to its inability to penetrate into the cuticle layer. Measuring the shear modulus as a function of humidity, changes showed an inverse relationship between humidity and shear modulus which was much more extreme with bleached hair than untreated hair. The shear modulus response to changing humidity was large and rapid indicating that moisture has a dominant effect on the cuticle layer and the cortex pf the fiber. ACKNOWLEDGMENTS The "Analysis and Quantification of Hair Damage" program was supported by a group of TRI corporate participants. We thank Mr. Carl Gorman and Mr. Peter Rockett for work on the original and next generation torsion pendulums (see Fig. 10 below). REFERENCES (1) D. Persaud and Y. Karnath, Torsional method for evaluating hair damage and performance of hair care ingredients,]. Cosmet. Sci., 55(Suppl), S65-S77 (2004). (2) H. Bogary, Torsional properties of hair in relation to permanent waving and setting, J. Soc. Cosmet. Chem., 18, 575-589 (1969). (3) L. J. Wolfram and L. Albrecht, Torsional behavior of human hair, J. Soc. Cosmet. Chem., 36, 87-99 (1985). (4) C.R. Robbins, Chemical and Physical Behavior of Human Hair, 3rd Ed., (Springer-Verlag, New York, 1994), pp. 189.