Chapter 10 341 The shape of an isotherm is also of interest as it provides information on the nature of interactions. In the field of adsorption science, the relationship between the water content of hair and the relative humidity would be classified as a Type II isotherm, which itself is a combination of a Type I (representing reasonably strong adsorption) and a Type III (representing weak interaction).7 Figure 7 shows a schematic of this occurrence. The idea of different domains of adsorbed water within a substrate was prevalent in the related field of textile materials during the early-to-mid 20th century. In 1926, Hedges8 used the aforementioned differences in adsorption isotherms as a function of temperature to calculate adsorption energies for water on silk and cotton. He determined that stronger energies were obtained when adsorption occurred on a relatively dry substrate, but progressively lower values resulted when further adsorption occurred on top of already significant water content. This led to postulation of three distinct stages of adsorption “with no sharp demarcation between Figure 6. Adsorption isotherms for virgin and chemically-damaged hair