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 mum under conditions of maximum contact load in t he range of 150-600 muN and loading/unloading rates between 7.5 and 600 muN /s. The elastic modulus of each polymer was determined from the unloading m aterial response using the compliance method, whereas the hardness was calc ulated as the maximum contact load divided by the corresponding projected a rea, obtained from the known tip shape function. It is shown that while the elastic modulus decrease with increasing indentation depth, the polymer ha rdness tends to increase, especially for the polymers possessing amorphous microstructures or less crystallinity. Differences in the material properti es, surface adhesion, and time-dependent deformation behavior are interpret ed in terms of the microstructure, crystallinity, and surface chemical stat e of the polymers. Results obtained at different maximum loads and loading rates demonstrate that the anoindentation technique is an effective method of differentiating the mechanical behavior of polymeric materials with diff erent microstructures.