204 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS -90.0 I I 20 p.m •CI Cr 10 prn 0 prn .•" •' .•1• CI p, rn 1CI p. rn 20 p.rn Figure 4. An AFM micrograph of scalp hair treated with a conditioner containing 1% zinc pyrithione same hair sample as that shown in Figure 1. Figure 6 shows an AFM micrograph of the mid-length region of unwashed scalp hair taken from a European brown-haired female, aged 25, with an average hair length of 20 cm. The cuticles were found to be poorly defined and, in some cases, damaged. Rough deposits were observed on hair surfaces, giving the hair an overall dull appearance. Washing the hair with a conventional sodium lauryl sulphate shampoo, followed by treatment with a conditioner containing dimethicones, resulted in improved cuticle definition and a smoother appearance (Figures 7a and 7b, different areas and not the same area as shown in Figure 6). The AFM images presented so far represent variations in topography across the hair surface. However, AFM is able to provide other information, such as variations in local physical properties, relative friction, hardness, and adhesion. Frictional properties can be obtained by mapping small variations in the twisting motion of the AFM cantilever as it raster-scans across the hair surface (17). The information from this "derivative" tech- nique, known as lateral force microscopy (LFM), can be acquired at the same time as topographic information and can be conveniently displayed alongside. The AFM mi- crographs in Figure 8 show (a) a topographic image and (b) a lateral force image. In Figure 8a, as in all the micrographs so far presented, the image is left-shaded, i.e., a light source can be imagined being positioned toward the left-hand side of the image, so that

AFM FOR STUDIES OF HUMAN HAIR 205 -900 ø 90.0 ø 20 lO I•rn 0 pm 0 gm 10 pm 20 pm Figure 5. An AFM micrograph of scalp hair, treated with a conditioner containing 1% zinc pyrithione, imaged in distilled water. all bright features correspond to features on the left of a plane drawn perpendicular to the plane of the paper in Figure 8b, bright areas correspond to areas of high relative friction, such as the rough endocuticle, with darker areas corresponding to smoother features, such as the exocuticle. With appropriate optimization, the contrast could be used to probe local frictional variations on an exocuticle surface at even higher resolution. CONCLUSIONS This paper reports the use of atomic force microscopy for obtaining fine structural information on human hair surfaces. The value of the technique has been clearly dem- onstrated, and in the area of cosmetics, AFM shows almost unlimited potential for investigations requiring detailed knowledge of the processes involved in hair cleansing, swelling, damage, and repair. ACKNOWLEDGMENTS The author thanks Miss Jacqui Mead for providing hair samples and helping to prepare this manuscript.