Analysis of water distribution in delipidated human hair by small-angle neutron scattering (SANS).

Objective It is known that damaged hair has a part of its internal structure damaged and its water absorption and desorption behavior are different. In recent years, it has been reported that internal lipids play an important role in the adsorption and desorption of water to the hair. Therefore, we investigate whether the water distribution in hair and the amount of internal lipids are related. Methods To investigate the effect of internal lipid on water distribution, we prepare human hair samples with and without a partial lack of internal lipids. Internal lipids have been removed using formic acid. The distribution of D2O in the hair is investigated using small angle neutron scattering (SANS) under the wet and dry conditions of each hair sample. Results It is found from the obtained SANS data that formic acid-treated hairs tended to have fewer 40A-sized water clusters that were periodically present along the fiber-axis in the wet condition. On the other hand, in the dry condition, there were no differences in water distribution between samples. Conclusion These observations are believed to have been caused by the reduction of 40A-sized water clusters existing on the constituents removed by formic acid treatment, especially the hydrophobic (lipid) constituent tissues. Consequently, it is clarified that internal lipids are deeply involved in the state of water distribution on hair in wet conditions.