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Surface characterization of human hair by atomic force microscopy in the imaging and F-d modes
Journal article   Peer reviewed

Surface characterization of human hair by atomic force microscopy in the imaging and F-d modes

Jolanta A Blach, W Loughlin, Gregory S Watson and S Myhra
International Journal of Cosmetic Science, Vol.23(3), pp.165-174
2001
DOI: https://doi.org/10.1046/j.1467-2494.2001.00080.x
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https://doi.org/10.1046/j.1467-2494.2001.00080.xView
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Abstract

aqueous exposure atomic force microscopy human hair surface properties surface structure
Surface structure and surface mechanical properties of human hair have been characterized by atomic force microscopy in the imaging mode and by force vs. distance. F-d, analysis. The effects of treatment by commercial conditioner/shampoo or by aqueous exposure have been investigated. The cuticular structure has been imaged at medium resolution: longitudinal striations with lateral spacings of 150-350 nm and vertical corrugations in the range 2-8 nm were observed at higher resolution. The features are similar to those observed for untreated wool fibre. Both adventitious debris/contamination and residues from cosmetic treatment can be imaged with resolution in the low-nanometre range. Removal of the cuticular surface layer from treatment with alkali solution, and subsequent imaging, revealed a fibrous substructure. F-d analysis of the surface is a rich source of spatially resolved mechanical and chemical information. Surface stiffness, and an equivalent Young's Modulus, E, can be inferred from the shape of the 'approach' tip-to-surface contact curve. A value of E of ≈10 MPa was obtained for untreated hair. During aqueous exposure for 1 h the stiffness and modulus decreased by approximately a factor of 10. The discontinuity seen at 'lift-off' during the retract half-cycle of F-d analysis represents a measure of tip-to-surface adhesion. Adhesion decreased during aqueous exposure and was below the level of detectability after 1 h. Likewise, treatment by conditioner had the effect of lowering adhesion. High resolution F-d data revealed features that are consistent with the presence of a thin and readily compressible surface layer, probably analogous to the surface lipid layer on untreated wool fibre.

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