Abstract
In order to investigate the influence of urea on the diffusion of polyethylenimine(PEI) into human hair,cross sectional samples of white human hair treated with PEI solutions containing urea and no urea,were prepared.In particular,a method for analyzing the diffusion behavior of PEI in the bleached human hair was developed,in which the PEI parts in the cross-sectional samples were dyed with orange orange II and the cross sections were examined at a wavelength of 487 nm (λmax of orange II) with a microspectrophotometer.
The penetration of PEI into virgin hair and bleached hair clearly increased by adding 20 wt % urea in all cases despite varying PEI molecular weights (600-20000) except for the virgin hair sample treated with PEI (Mw: 20000). Also, the diffusion pattern of PEI at pH 11.1 showed Fickian type characteristics regardless of adding urea or not. The diffusion coefficient of PEI (Mw: 600), with urea added, increased 2 times in comparison with that of PEI, with urea not added. From these experiments, it was demonstrated that urea acts as a penetration accelerator for PEI.
