Scanning probe microscopy examination of the surface properties of keratin fibres

A Scanning Probe Microscope (SPM) was used to investigate the mechanical properties of the surface of hair and wool fibres. Using stiff cantilevers, penetration was achieved on the fibres under ambient conditions and at increased relative humidity (RH). The Young's modulus of the exocuticle was estimated to be 2.1 GPa under ambient conditions, decreasing to 0.6 GPa at 96% RH. Contrary to findings by other authors [Crossley, J.A.A., Gibson, C.T., Mapledoram, L.D. , Huson, M.G., Myhra, S., Pham, D.K., Sofield, C.J., Turner, P.S., Watson, G.S., 2000. Atomic force microscopy analysis of wool fibre surfaces in air and under water. Micron 31, 659-667; Gibson, C.T., Watson, G.S., Mapledoram, L.D., Kondo, H., Myhra, S., 1999. Characterisation of organic thin films by atomic force microscopy-application of force vs. distance analysis and other modes. Applied Surface Science 144-145, 618-622; Blach, J., Loughlin, W., Watson, G.S., Myhra, S., 2001. Surface characterization of human hair by atomic force microscopy in the imaging and f-d modes. Journal of Cosmetic Science 23, 165-174], the surface lipid layer could not be penetrated using soft cantilevers in force-distance (f-d) mode in water. Attempts were made to remove the lipid layer from the surface both physically and chemically so as to examine the influence of the lipid on f-d measurements. Using both techniques, it was not possible to remove lipid without damaging the fibre, suggesting that the lipid is an integral part of the surface rather than a discrete surface layer. Adhesion measurements on the surface of wool, nylon and polyethylene, showed that in water and at high RH, the surface of keratin fibres is more akin to a polyamide. At low RH and in liquid paraffin, the surface is more akin to a hydrocarbon, suggesting it is capable of altering its structure in response to different environments.