Nanoindentation of nanocomposites

The spray coatings were dried and the dried coatings were subjected to nano-indentation using a nano-indenter made by Hysitron. Contact area was calibrated by using silica and polycarbonate of known modulus and hardness. This work on nano-indentation of polycarbonate containing nano-particles of silica shows that there is an increase in modulus and hardness up to a certain concentration threshold in concentration. As the level of silica increases beyond a threshold level, aggregates form which results in weakening of the structure. Polymer silica interface is found to be weak as silica is non-interacting promoting interfacial slip at silica -matrix junctions. At critical stress level for silica –polymer interfacial slip is reached and filler-matrix debonding (sliding) is activated resulting in a decrease in the composite’s stiffness.
Departure from the analytical composite models is analyzed in terms of interface adhesion between nanofiller and polymer matrix. Results on polycarbonates are compared with those of nanocomposites of polyesters where the effect of composite hardness and modulus depended on dispersion of nano-filler in polycarbonate or polyester.. Experimental results are compared against analytical models