Nanomechanical properties of polyaniline and azo polyelectrolyte multilayer films

Nanomechanical properties of multilayer films constructed of polyaniline (PANI) and azobeneze-containing polyelectrolytes (PNACN and PPAPE) were studied by using nanoindentation method. The multilayer films were prepared by the electrostatic layer-by-layer self-assembly through alternately dipping in the polymer solutions. The multilayer films deposited onto the glass slides after proper dry were used for the nanomechanical property testing. The nanomechanical measurement indicated that the PANI/PNACN and PANI/PPAPE multilayers possessed the mean elastic modulus of 5.42 GPa and 4.35 GPa, and hardness of 0.26 GPa and 0.18 GPa, respectively. The nanoscratch properties of the PANI/PNACN and PANI/PPAPE multilayer films were also measured. The critical loads of PANI/PNACN and PANI/PPAPE films were 103.52 mN and 100.59 mN. The degree of electrostatic cross-linking in the multilayers could be altered by exposing the films to aqueous solutions with different pH values. As a result, the modulus and hardness of the multilayer films were changed through the solvent treatment. Both modulus and hardness of the PANI/PNACN films obviously increased after dipping the multilayer films in solutions with pH in a range from 9 to 11.