Particle Dispersion
In the case of clays and polycarbonates, the dispersion of particles in paper coatings can be readily established from AFM images. Figure 6 is of an Astr-Plus/Carinal 95 coating. In this image the positions of kaolin hexagonal platelets are clearly visible. Besides measuring surface topography, images of other surface physical properties such as hardness and adhesion are measurable with the AFM. As an example, in the AFM it is possible to vibrate the stylus as it is scanned over a surface. Then by measuring the change in phase between the modulating signal and the signal coming from the photo-detector, images of surface hardness are obtained. In this technique, both the surface topography and surface hardness image are acquired simultaneously. Figure 6: AFM image of Astr-Plus/Carbinal 95 coating. This "engineered" coating is comprised of kaolin in a narrow particle size distribution and an ultra fine ground calcium carbonate with a latex binder. This technique is ideal for visualizing the location of polymer material used in paper coatings. Figure 7 shows the topography image and hardness image of a commercially available paper coating. The dark areas in the image show the locations of the polymer material in the coating.  Figure 7: Left - Topography . Right - Hardness image of a comercially available paper coating. These images are measured simultaneously. The gray scale in the hardness image represents the surface hardness.
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