Nanotribological characterization of human head hair by friction force microscopy in dry atmosphere and aqueous environment.

Friction force microscopy was employed for the tribological investigation of human head hair in two different environments: a dry atmosphere and de-ionized water. The fibers were immobilized by embedding them in indium. The effects of bleaching, conditioning, and immersion in methanolic KOH were quantified in terms of the relative coefficient of friction (μ). The virgin fibers were clearly distinguished in terms of friction coefficient from the chemically damaged ones in both environments, while all categories of hair exhibited higher friction coefficients in the aqueous environment. Secondary ion mass spectroscopy was used as a complementary technique to examine the presence of fatty acids on the cuticular surface of the different categories of hair as well as the conditioner distribution. Neither bleaching nor 30 min treatment in methanolic KOH was found adequate to completely remove the fatty acids from the fibers' surface. Conditioner species were detected along the whole cuticular surface.