Investigation of mechanical and creep properties of polypyrrole by depth-sensing indentation

In this study, we used depth-sensing indentation (DSI) technique to investigate some mechanical properties (reduced elastic modulus, indentation hardness, and creep) of polypyrrole (PPy) conducting polymer obtained with different support electrolyte concentration. The influence of support electrolyte concentration on these parameters was also determined. The order of doping degree of the samples was determined by cyclic voltammetry. The indentation load-displacement curves of the samples were obtained under different peak load levels with a 70 s holding time at maximum load. Reduced elastic modulus and hardness values were determined by analysis of these curves using the Feng-Ngan (F-N) and Tang-Ngan (T-N) methods, respectively. Both reduced elastic modulus (E-r) and indentation hardness (H) exhibited significant peak load dependence, i.e., indentation size effect (ISE). It was found that both E-r and H values decreased as the support electrolyte concentration was increased. This was explained by an increase in the free volume as the doping degree was raised. The creep behavior of the samples was monitored from the load holding segment of the load-unload curves. It was found that creep increases with the increasing support electrolyte concentration.