368 JOURNAL OF COSMETIC SCIENCE Figure 18. Bending and failure of adhesion by knotting a hair fiber (1). Photograph reproduced with permission of Springer-Verlag. such as sodium deceth-3 sulfate or sodium laureth-3 sulfate do not produce this failure as readily as TEA dodecyl sulfate or sodium lauryl sulfate. Cationic surfactants such as cetrimonium chloride and benzalkonium chloride provide the most failure and scale lifting when applied alternately with salts of lauryl sulfate. In general, those combina­ tions of anionic and cationic surfactants that most readily form water-insoluble cationic­ anionic complexes produce the most failure, while those that do not tend to form water-insoluble complexes, such as sodium deceth-3 sulfate with tetradecyl trimonium chloride, do not tend to produce this failure. Since permanent waving is essentially a prerequisite to this condition, and perming produces this effect more readily than bleaching, we believe that cleavage of the thioester linkage between the outer beta layer and the hydrophobic keratin protein (Figure 2B) is involved because this bond has been shown to be sensitive to strong nucleophiles like amines and mercaptans (3,22) (see Figure 20). This reaction of TGA in the cuticle­ cuticle CMC weakens the outer beta layer by cleaving thioester linkages through nu­ cleophilic displacement with TGA, creating a hydrophilic structure from a hydrophobic one at the cuticle membrane region of fatty acid attachment (hydrophobic keratin protein (b) in Figure 2A) rather than at the delta layer attachment (see the monolayer model in Figures 2B and 20). The next step involves penetration of cationic surfactant into this site and bonding by salt linkage to the newly formed anionic sites in this weakened region. Subsequently, anionic surfactant penetrates and reacts to form an

ADHESION FAILURE IN HAIR 369 Figure 19. Adhesion failure from alternating treatments with anionic and cationic surfactants on previously permed hair (1). Photographs reproduced with permission of Springer-Verlag. insoluble complex with the sorbed cationic surfactant (Figure 21). After several repeti­ tive anionic-cationic reactions, buildup of a hydrophobic anionic-cationic complex oc­ curs, producing adhesion failure at this site. These reactions will produce beta­ membrane failure rather than beta-delta failure (see Figure 11). The fact that scale lifting occurs from the reaction ofTGA-treated hair more readily than with bleached hair suggests that this effect is governed more by reaction with the thioester linkage than with the disulfide grouping. Nevertheless, the net effect is to weaken the CMC and increase its tendency to fail under stress. SUMMARY AND CONCLUSIONS Although adhesion failure in hair fibers can occur inside cuticle and cortical cells, it frequently occurs in the cell membrane complex (CMC), often involving interlayer bonding. Therefore, a model of the CMC is presented, based on prior research in which we propose interconnecting bonds between the different layers to assist in our interpre­ tation of hair fracturing mechanisms for cuticle chipping, deep transverse cuticle cracks,