Chapter 10 343 It is also necessary to ponder where these adsorption sites reside in the complex hair structure. In 1959, Feughelman12 linked the predominantly radial swelling that accompanies moisture uptake of keratin fibers with X-ray studies that revealed how the alpha- helical protein structure of the microfibrils is essentially unaffected by this occurrence. This led to his proposal of a “two-phase model,” where macrofibrils are considered to comprise of crystalline, water-impenetrable, rod-like microfibril structures embedded in a water-swellable, amorphous matrix. The actual adsorption sites for water molecules on the protein chains would seem to involve both hydrophilic amino acid functional groups and the peptide bond itself. The high incidence of peptide bonds led to suggestions of this being the primary contributor,13 although studies have shown how chemical manipulation of functional groups will alter the adsorption isotherm.14 Therefore, as water enters the matrix, it solvates these species and diminishes the ability to form secondary structuring, such as hydrogen bonding and salt bridges. In short, the mechanical properties of dry hair are supported by contributions from both the crystalline and amorphous constituents, but the matrix involvement is essentially eliminated in the wet state (see Chapter 7, Figure 1). An analogy to this occurrence involves a common household sponge, which possesses significant stiffness and rigidity when dry, but relinquishes these properties when wet. If the sponge is allowed to dry in a given confirmation, it will retain this new shape until re-wetted. Similarly, temporary hair styles can be attained by heat- related techniques (e.g. hair driers, flat irons, curling irons, heated Figure 8. Schematic of multilayer water adsorption