Caracterização por espectroscopias Raman e no infravermelho e microscopia de cabelos tratados com produtos cosméticos

Abstract

Hair studies have evolved significantly over the years and vibrational spectroscopic techniques, such as Raman and infrared, have become great allies. Understanding this evolution, this work aimed to study the chemical structures of natural hair and hair treated with cosmetics, both in more superficial regions of the fiber (cuticle region) and internally (cortex and medulla region), and to analyze the effect of permeation of such products in hair samples. Through vibrational spectroscopy it was possible to explore the surface and internal characteristics of the yarn, as well as to verify its interaction with bleaching products and products that propose a better quality for the fiber. Through the Raman spectra it was observed that the band at 509 cm-1 , attributed to the S-S stretching, has greater intensity in the cuticular region, due to the higher concentration of cystine in this area. On the other hand, the C-C band at 932 cm-1 , which is attributed to secondary α-helix conformation, is found mainly in the cortex region, confirming that the central region of the hair is composed largely of α-helix structure. Amide vibrational modes, assigned to protein secondary structures, contributed to detecting a greater accumulation of the β-sheet conformation and disordered structure in the cuticle. These techniques also provided the identification of discolored samples, since the vibrational spectra showed an increase in the intensity of the band assigned to the cysteic acid residue, around 1044 cm-1 . After bleaching, ten different cosmetic treatments were applied individually to the samples, and it was possible to observe the diffusion of four of these products inside the hair. It was found that the applied products permeated mainly the cuticle region, with less diffusion into the cortex. Fluorescence microscopy showed that in bleached samples the dye was able to diffuse throughout the hair structure. However, when the dye is applied to samples treated with certain cosmetics, fluorescence is detected only in the cuticular region, indicating that the product acted as a barrier in diffusing the dye. Thus, vibrational spectroscopy has proven to be a valuable tool for studying cosmetic permeation into the hair fiber and for analyzing its surface and internal structure.