Rubbed, topography

The PMMA surface was first imaged before rubbing, as shown in Fig. 7.20. The image on the left shows the topography, while the one on the right shows the NC EFM signal. 

Fig. 7.22. Topography (left) and NC EFM image (right) of the PMMA surface rubbed ten times [86].

No traces of topographical deformations or electrostatic charge domains are visible. After rubbing the sample, we obseived variations in both the surface topography and charged domains oriented along the rubbing direction (Fig. 7.21). 

Fig. 7.25. Topography (left) and NC EFM image (right) of the PMMA rubbed once in one direction and then once again in a direction at an angle of about 45 degrees with respect to the first one [86],...

In order to get information on wear mechanisms, it is necessary to complement the determination of wear volume by a structural characterization of the worn surface. Friction and wear cause characteristic changes of surface topography and of the microstructure in a thin zone below the rubbing surface, which can give information on prevailing wear mechanisms. Additional information is obtained by an analysis of the size and composition of the wear particles. Electron microscopy (SEM, TEM) and surface analysis methods (AES, XPS, etc) are generally used for this purpose. 

Figure 4. The three main substrate classes (a) smooth surfaces on which surface molecules have a definite orientational distribution (represented surface obtained on a rubbed polyimide film [52]) (b) interpenetrable surfaces of dangling chains (c) topographies (represented grooved surface) with a favorable (left) and unfavorable director field R. In all cases, a is the macroscopic anchoring direction.

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