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Analytical Chemistry

Surface Chemistry Of Becoming A Blonde

Atomic probe microscopy reveals how hydrogen peroxide alters hair on the nanoscale

by Matt Davenport
September 22, 2014 | A version of this story appeared in Volume 92, Issue 38

Credit: Langmuir
AFM and FTIR revealed how bleaching exposes SO3 groups on hair’s keratin surface.
Optical and AFM image of natural and bleach hair.
Credit: Langmuir
AFM and FTIR revealed how bleaching exposes SO3 groups on hair’s keratin surface.

Bleaching agents such as hydrogen peroxide lighten hair by oxidizing its melanin pigment. But the agents also induce other chemical changes, not all of which are desirable or understood. Getting to the root of these modifications could help scientists develop better products for protecting or repairing human hair. Researchers led by Gustavo S. Luengo of personal care products manufacturer L’Oréal and Sabri Akari of contract research firm NanoCraft Coating have launched what they say is the most comprehensive study of hair surface chemistry to date (Langmuir 2014, DOI: 10.1021/la500461y). The team showed that H2O2 strips hair of its natural hydrophobic lipid coating, exposing charged sulfite groups of cysteic acid molecules in micro- and nanoscopic clusters. FTIR spectroscopy allowed the researchers to identify the molecules bound to the keratin surface of the hair cuticle. They also scanned hairs with atomic force microscopy (AFM) using chemically modified tips for the first time. The researchers used methyl-terminated tips to map a hair strand’s hydrophobicity and aminated tips to probe its electronic charge profile with nanometer resolution, revealing the size and spacing of damaged domains. These results, Luengo says, “help us understand the surface of hair so we can better take care of it.”


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