683 THE MATRIX REVISITED which is in line with the idea of globular KAPs in the matrix, in accordance with the models proposed by Crewther (29) and later by Feughelman (36) and critically summarized by Hearle (37). The model of the matrix supported by these results is similar to the original beaded model of Crewther (29). Moreover, the TET results indicate that the grains exhibit a certain order at the nanoscale, which implies organization of the proteins and not a random packing of chains associated with densely cross-linked disulfide bonds (35). The model of hair given in Figure 10 summarizes these results and suggests that there is, still, more to investigate concerning the structure of matrix. Figure 9. Matrix beaded-chain model describing the effects of the bleaching process on hair (18,34) Figure 10. Hair model with a grainy matrix (38).

684 JOURNAL OF COSMETIC SCIENCE CONCLUSION The work reported herein attempts to demonstrate how experiments performed in the wet state yield only part of the story regarding hair’s physical properties. Specifically, such experiments contain no contribution from the amorphous KAPs, that is, the matrix. Yet, this structure can be the dominant contributor to certain properties, such as fiber stiffness. Furthermore, the results from dry-state experiments, which do include matrix contributions, can produce outcomes contrary to well-established beliefs. For example, damaging chemical treatments can raise hair’s dry-state modulus and produce higher dry- state protein denaturing temperatures. Approaches have been described for modeling the contributions of the various internal structures to hair properties, while similarly incorporating the sizable effects of water content. To this end, experiments at low humidity (i.e., low water content) contain higher contributions from the innate matrix structure, for which the disruptive effects of moisture are minimized. Testing is rarely performed under these conditions, and new insights may be waiting in experiments performed under these conditions. For example, Figure 11 shows results from modulus versus humidity experiments that were performed on different hair samples obtained from a variety of individual donors. These curves superimpose and suggest no differences at high water content, but considerable divergence occurs at low humidity. The properties of hairs obtained from individual heads can be substantially altered by habits and practices yet, all of our donors reported no use of chemical treatments. Moreover, the three behaviors shown in Figure 11 were repeatedly encountered, whereas more random outcomes would presumably be expected if the hairs exhibited substantial contributions from the diversity of consumer practices. In accordance with the principles outlined herein, these mechanical properties imply differences in the internal structures of the hairs from these individuals—particularly in the structure and morphology of the amorphous matrix. This presumption is outside the 0 20 40 60 80 100 1e+9 2e+9 3e+9 4e+9 5e+9 Young’s modulus as a function of RH Relative humidity (%) Behavior 3 Behavior 2 Behavior 1 Figure 11. Differing shapes for Young’s moduli versus RH curves for single-source hairs obtained from different individuals. Yongsmodls