682 JOURNAL OF COSMETIC SCIENCE Crewther stated that there is an “essentially uniform interaction between the microfibrils and the high-sulfur proteins of the matrix” (29). Chapman came to a similar conclusion regarding disulfide links between a less-ordered matrix and the KIFs (30). These works suggest that there is an interface between the matrix and the KIFs. In other words, it appears that the two-phase model (see Figure 1) needs to be upgraded to include three phases. Solid-state nuclear magnetic resonance (NMR) experiments involving hair, as well as DSC studies on hair at different pH values, also suggest that a three-phase model for hair (shown in Figure 8) could better explain the properties of hair (31,32). Assuming the existence of an interface between the matrix and the KIFs also necessitates adjustments to the meanings of peak temperature and enthalpy, particularly for the values recorded from the wet DSC of hair, from those given in Figure 5 to a more complex picture, suggested in Figure 8 (22,33). Crewther also suggested that the protein globules (KAPs) of the matrix, which contain a large number of internal disulfide cross-links, covalently linked to each other to form a “loose, randomly arranged or only partly oriented, network of beaded chains” (29). This model of a beaded matrix is further supported by solid-state NMR data (34), and as depicted in Figure 9, it explains well the effects of the bleaching process (18,34). Recent experiments measuring the transport of heat through hair fibers by a transient electrothermal (TET) technique (35) also suggested a grainy nanoscale matrix structure, Figure 8. Three-phase model and DSC measurements that reflect the states of the model’s three components (22,31–33).

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).