A correlation between the Wolf-Wilburn scale and atomic force microscopy for anti-scratch resistance determination

The quality of coatings is continuously improving due in part to the irruption of nanotechnology in material science, which has made it possible to manufacture novel nanocomposites. Similarly, the methodologies to measure the mechanical properties of polymer-based nanocomposite coatings are changing. However, a real standard to measure, for example, anti-scratch resistance using equipment such an Atomic Force Microscope (AFM), does not exist due to the strong influence of operational conditions on the final results. This means it is impossible to compare the results of different authors. Moreover, traditional methodologies used in industry, like the Wolf-Wilburn Test, are not able to measure the hardness of novel composites since they can go out of scale. In this work, an AFM is used to make nano-scratches in urethane-acrylate coating surfaces with known Wolf-Wilburn scale values, calculating the anti-scratch resistance. These data are correlated through linear regression. This correlation could be used to obtain the Wolf-Wilburn values from the width of groove made on the polymer surface by the AFM tip. Thus, this work present a potential way to extend the Wolf-Wilburn scale using AFM for those coatings that could not be measurable with Wolf-Wilburn Test.