Distribution and Localization of Hydrophobic and Ionic Chemical Groups at the Surface of Bleached Human Hair Fibers

Abstract

A chemical mapping with high lateral resolution using an atomic force microscope in the pulsed force mode with chemically modified tips, introduced as "dynamic chemical force microscopy" (dCFM), was carried out to investigate the chemical properties of the cuticle of human hair and its changes following an oxidative treatment. Chemically modified atomic force microscopy (AFM) tips, CH3- and NH2-terminated, were applied to achieve a defined chemical contrast (hydrophobic and ionic) in aqueous medium. A comparative Fourier transform infrared spectroscopy-attenuated total reflection identified the dominant chemical groups of the surface vicinity of the hair fiber resulting from the bleaching process. The combined experimental results lead to the conclusion that the hydrophobic top layer is partially removed after bleaching, resulting mostly in hydrophilic SO3(-) end groups at the top of the surface of the hair, with a mean surface density "δ(mean)" of negatively charged groups of approximately 2.2 molecules/nm(2), corresponding to ∼600 μg/m(2) cysteic acid. This indicates that thioester bonds are disrupted and fatty acids are removed as a result of cysteine oxidation. At the molecular level, our results indicate a clustered "self-assembled monolayer" alignment of cysteic acid with a crystal-like structuring, reminiscent of the "fluid mosaic model of cell membranes", with a surface energy of approximately 0.04 N/m. Despite previous extensive works of AFM on human hair, this is, to our knowledge, the first time that the hydrophobic and ionic sites at the top surface of hair have been imaged at the nanoscale with dCFM.

Atmospheric Pressure Plasma Jet Treatment of Human Hair Fibers

“…The top layer can be stripped off via processes such as peroxide treatment [25][26][27], or ultraviolet exposure [26]. During the chemical process, i.e., bleaching, the chemistry of the top lipid layer and, when exposed, underlying proteins are altered [19] resulting in the changes in surface energy and hydrophobicity [24,25], luster [28], and mechanical properties [21].…”

“…During the chemical process, i.e., bleaching, the chemistry of the top lipid layer and, when exposed, underlying proteins are altered [19] resulting in the changes in surface energy and hydrophobicity [24,25], luster [28], and mechanical properties [21]. The surface of a bleached hair fiber has lower cysteine and higher cysteic acid (-SO 3 -) contents due to the removal of the 18-MEA layer and oxidation of cysteine groups [19].…”

Physicochemical Aspects of the Performance of Hair-Conditioning Formulations

“…The study of the adsorption processes of polymer-surfactant systems onto solid substrates is of interest for the cosmetic industry. This is because the performance of shampoo and conditioners is related to the deposition of polymer-surfactant complexes onto the surface of hair fibers, with the latter being a relatively large effective surface with an extraordinary chemical and topographic complexity [8,95]. The adsorption of the polymer-surfactant complexes onto solid surfaces depends on various factors such as the properties of the polymer (charge, molecular weight, concentration), the surface (charge, surface energy) and the solution (pH, temperature, solvent quality, ionic strength) as well as the nature and concentration of the surfactant [9,79,[96][97][98].…”

Nanoparticle Probes for Quantifying Supramolecular Determinants of Biosurface Affinity

“…[8] Most understanding regarding interactions of synthetic and bio-system with biosurfaces is on the charge of each components, such as electrostatic forces between two opposing charged systems. [9,10] The supramolecularly competitive aqueous environment in which these surfaces function makes multivalent interactions a prerequisite. For this reason, polymers have been used as multivalent platforms to study adsorption to hair and skin.…”

“…These observations are consistent with other studies where hair has strong interactions with cationic polymers used as conditioning agents, [9] and with amine-functionalized tips in AFM experiments. [10] Due to the negatively-charged hair surface, cationic AuNPs can adsorb strongly to hair in deionized water via electrostatic interactions. The zeta potentials for 500 nM solutions of the anionic, zwitterionic and cationic nanoparticles were measured in ultrapure MilliQ water in equilibrium with air and were determined to be negative, neutral (slightly negative), and positive (Figure 1a).…”