Surface hardness of pristine and modified polyaniline films

The surface microhardness of conventional thermoplastics lie between 0.1 an d 0.6 GPa. The as-cast emeraldine (EM-25) base film of polyaniline (PANi) e xhibits a surface microhardness of about 1 GPa. The hardness is increased t o about 4 GPa in the highly cross-linked EM (EM-150) film. This hardness va lue is further enhanced to about 6 GPa after 1 cycle of acid-base treatment . The hardness of the EM-150 film can also be enhanced to about 8 GPa throu gh protonation or through reduction to the leucoemeraldine state. Surface m odification of the EM-150 films via graft copolymerization with acrylic aci d or styrenesulfonic acid readily gives rise to hard-surfaced PANi films ha ving microhardness values approaching 20 GPa. This surface hardness is comp arable to many of those reported for the very hard-surfaced conventional po lymers from high-energy ion-beam bombardments. The surface hardness of the surface-modified EM-150 film arises from the additional covalent bonding of the graft chains on the highly cross-linked EM-150 film surface and the ch arge-transfer interaction between the graft and the substrate chains.