Hydration dynamics of human fingernails: An ellipsometric study

We use spectroscopic ellipsometry to obtain the complex refractive index, n˜ = n + ik, of human fingernails. By studying the change of n˜ upon hydration and dehydration, we reveal three different time domains with typical time constants of 4, 150, and 3200 min. A simple model that takes into account the presence of one fast and one slow process is fully consistent with the observed hydration and dehydration dynamics. We attribute these processes to free water incorporated between the keratin filaments and water more tightly bound in keratin complexes, respectively. From our model we determine the hydration profiles of free and bound water during, both, hydration and dehydration. © 2002 The American Physical Society.