Indentation modulus and hardness of polyaniline thin films by atomic force microscopy

Polyaniline (PANI) thin films with different thicknesses have been deposited on indium tin oxide (ITO) coated glass substrates by electrochemical polymerization of the aniline monomer in H2SO4 aqueous solution. By using the tip of an atomic force microscopy (AFM) apparatus as an indenter, cantilever deflection versus sample vertical displacement curves have been acquired and analyzed for evaluating the contact stiffness, by using an approach analogous to that developed for standard depth sensing indentation (DSI) tests. After the calibration performed using a set of polymeric reference materials, indentation modulus and hardness of PANI films have been deduced as a function of the reached maximum penetration depth. By using a model originally proposed for the analysis of standard DSI measurements, indentation modulus and hardness values of only PANI are finally deduced from the corresponding apparent values measured for the film-substrate systems, although they have to be considered as semi-quantitative estimations, since the roughness of the films does not allow a certain determination of the local thickness in correspondence of the probed points.