Surface structures and adhesive-free adhesion characteristics of polyaniline films after modification by graft copolymerization

Surface modifications of emeraldine base (EB) films have been carried out via thermally induced graft copolymerization with acrylic acid (AAc), sodium salt of styrenesulfonic acid (NaSS),N,N'-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS), and acrylamide(AAm). The structure and chemical composition of each graft-copolymerized surface were studied by angle-resolved X-ray photoelectron spectroscopy(XPS). In all cases,the concentration of grafting increases with monomer concentration. Surface grafting with the four functional monomers also leads to a more hydrophilic EB film surface. Two graft-copolymerized EB film surfaces are capable of exhibiting adhesive-free adhesion when brought into direct contact in the presence of water and subsequently dried. This adhesive-free adhesion also exists between a surface-modified EB film and a similarly modified polytrafluoroethylene (PTFE) film from graft copolymerization. The development of the lap shear adhesion strength depends on the concentration of the surface graft, the adhesion (drying) time, the physical property of the substrate, the microstructure of the grafted surfaces, and the nature of the molecular interaction (dispersive, ionic, etc.) at the junction. Lap shear adhesion strength as high as 340 N/cm(2) was achieved between two EB films graft copolymerized with the amphoteric DMAPS monomer.