Depth-Sensing Nanoscale Deformation Experiments in Polymer Nanocomposites

There is currently a trend toward increased usage of polymeric materials as functional materials because they are likely to experience force in the nanometer range. Thus, we describe here nanoindentation experiments in a polymer nanocomposite system with different nanoclay content and compare with the pristine counterpart. A Berkovich nano-indenter was used to conduct nanoscale deformation experiments using a load of 1-5 mN. The nanoindentation contact properties of relevance to functional applications notably hardness, modulus, and adhesion forces were studied. The addition of 8 wt% of nanoclay to high density polyethylene led to an increase in the indentation hardness by similar to 30% and modulus by 25%. Furthermore, using load-displacement plots, the adhesion force between the indenter tip and the material's surface was measured. The adhesion force that is related to the stickiness of the surface was observed to decrease on the introduction of nanoclay in the polymer because of an increase in hardness and modulus of the nanocomposite, leading to a decrease in the area of interaction between the indenter tip and the probed surface. The resistance to nanoindentation of the nanocomposite is explained in terms of a shift in von Mises stress from the surface to the subsurface in the nanocomposite.