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Surfaces of wool scales are imaged using a scanning force microscope (SFM) and a field emission scanning electron microscope (FESEM). Atomic force microscope (AFM) images of wool fiber surfaces can be correlated with FESEM micrographs to provide complementary views of surface features. The AFM images are analyzed for scale height; on average there is a 21% increase when changing from air to water. The variability of scale height changes is large, and a model involving both swelling and scale movement has been proposed. Lateral force microscope (LFM) images show complementary information to topographic AFM images and reveal the effects of surface treatment not available with other imaging techniques. Such images of treated wool surfaces reveal major inhomogeneities in friction, which are interpreted as differences in chemical composition.Images of the fine details on the surfaces of wool fibers have traditionally been obtained using the scanning electron microscope (SEM) [ 24,25 ] . Due to their insulating nature, a conductive metal coating (typically 10 nm of gold) must be applied to fibers before they are inserted into the microscope vacuum. The image resolution detail is thus limited to 10 nm at best, and the fibers cannot be chemically treated for further studies after SEM imaging.Two recent developments have offered major improvements for imaging the surfaces of wool fibers. The field-emission SEM (FESEM) provides a sufficiently bright, focused electron beam to achieve satisfactory image quality at about 1 kilovolt beam energy, at which net charging of the wool surface does not occur. With fine metal coatings, detail down to the level of a few nanometers can be resolved on suitable samples. In contrast, the scanning force microscope (SFM), comprising an atomic force microscope (AFM) and a lateral force microscope (LFM), scans a fine mechanical probe across the sample surface, &dquo;feeling&dquo; the topography and the frictional forces [ 18 ] . Resolution is limited by the surface roughness of the sample being imaged and by the effective diameter of the tip (typically 100 nm). Thus, while atomic resolution can be achieved through the interaction of atomic sized protrusions on the tip with very smooth, flat surfaces ( e.g., on mica), the resolution on a rough surface will be determined by the typical feature heights and their spacing relative to the scanning tip dimensions.The SFM is very useful for imaging biological samples because it is nondestructive to the sample and can operate in both air and liquid. For wool, which is frequently exposed to both air and aqueous environments during processing, this is particularly important because of the well known sensitivity of many of its properties to moisture [ 1 ]]. In particular, felting of wool is worse in water, and there is a common belief that the scales are more prominent when wet [ I 4 ] . The advent of the environmental SEM has produced results indicating that the scales probably are more pronounced when wet, but not under saturated water vapor conditio...

Contact angle data from various sources in conjunction with the Israelachvili and Gee equation derived for chemically heterogeneous surfaces are used to describe the wool fiber surface/liquid/air interface. A diagram representing surface compositions consistent with this data is constructed based on the assumption that the wool fiber surface chemical moieties consist of methyl, methylene, and hydrophilic groups. The results from these analyses indicate that the fiber/liquid/air interface is at variance with a current surface model (based on chemical analysis) that predicts a simple methyl-like composition. The paper concludes that the wool fiber surface cannot be described as chemically homogeneous.