Peter L. Drzal

Metrology for characterizing scratch resistance of polymer coatings

Current methods for scratch resistance assessment are often based on “relative but not quantitative” types of measurements, such as visual inspection, gloss changes, and changes in gray scale level or lightness. Most results are used for qualitative assessment purposes, which result in the lack of a repeatable and reliable standardized test method for the polymer materials community. To implement a scientifically based standardized test method for quantifying scratch resistance, it is vital to understand the relationships between material mechanical properties, morphology, and appearance (optical properties) of surface and subsurface deformation. In this article, preliminary results from a scratch testing protocol to identify the “onset” of plastic deformation in poly(methyl methacrylate) and poly(propylene) commercial samples are presented. Recent advances in optical scattering measurements to identify the onset of plastic deformation by analyzing specular and off-specular intensities are also presented.

Viscoelastic Characterization of Polymers Using Dynamic Instrumented Indentation

Dynamic nanoindentation was performed on a poly(methyl methacrylate, PMMA), and two different poly(dimethyl siloxane, PDMS) samples having different crosslink densities. Comparison was made between dynamic nanoindentation and rheological instrumentation measurements in the glassy and rubbery plateau regions of polymeric materials. Excellent agreement between bulk rheological data and dynamic nanoindentation data was observed for the two glassy materials and the less compliant of the two PDMS samples. Results were divergent for the more compliant PDMS sample.