Short Poster Lecture
Colouring of hair by biological substances, in particular plant dyes such as Henna or Indigo, are widely used procedures to achieve a variation in the appearance and a specific look of many people. Colouring, however, is a complicated process, where the substances have to infiltrate a material with different structures such as the cuticle, the cortex and the medulla. As hair is also a hierarchical material, it has additional structural features at different length scales, from atomic to the nanoscale. This is due to by keratin coiled-coils forming intermediate filaments with a diameter of 7 to 10 nm. At this size level, we investigated the effect of colouring dyes on the nanostructure by small-angle and wide-angle X-ray scattering techniques. The structural data are correlated to mechanical data from tension tests, and a positive or negative effect on the tensile strength is discussed.