Nanomechanical Properties of Polymers Determined From Nanoindentation Experiments

The nanomechanical properties of various polymers were examined in light of nanoindentation experiments performed with a diamond tip of nominal radius of curvature of about 20 μm under conditions of maximum contact load in the range of 150–600 μN and loading/unloading rates between 7.5 and 600 μN/s. The elastic modulus of each polymer was determined from the unloading material response using the compliance method, whereas the hardness was calculated as the maximum contact load divided by the corresponding projected area, obtained from the known tip shape function. It is shown that while the elastic modulus decreases with increasing indentation depth, the polymer hardness tends to increase, especially for the polymers possessing amorphous microstructures or less crystallinity. Differences in the material properties, surface adhesion, and time-dependent deformation behavior are interpreted in terms of the microstructure, crystallinity, and surface chemical state of the polymers. Results obtained at different maximum loads and loading rates demonstrate that the nanoindentation technique is an effective method of differentiating the mechanical behavior of polymeric materials with different microstructures.