Surface-graft polymerization of doped polyaniline with hydrophilic monomers

Polyaniline (PAn) samples doped with different types of protonic acids with or without argon plasma pretreatment were subjected to graft polymerization with acrylamide (AM) or acrylic acid (AA), using (NH4)2S2O8 as initiator. The structure and chemical composition at the PAn surface were characterized by reflection FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Conductivity and water contact angle of the PAn samples were also studied. SEM micrographs indicated the appearance of flocculent matters on the PAn surface after graft polymerization. As the amount of flocculent matters increases, the water contact angle decreases or the hydrophilicity increases. C 1s core-level spectra in XPS showed an increase of C atoms for COOH or CONH2 after plasma pretreatment and graft polymerization, and N 1s core-level spectra indicated that after acid doping or graft polymerization, proportion of nitrogen atoms in the form of N+ increases obviously, whereas nitrogen atoms in the form of amine decreases seriously. Both the amount of surface-grafting and hydrophilicity of the PAn samples were enhanced by plasma pretreatment. Conductivities of all the doped PAn samples decreased within one order of magnitude, after the argon plasma pretreatment and surface-graft polymerization with AM or AA. After both surface modifications, the HNO3 and HCl doped PAn samples showed higher conductivity than other samples, whereas, the H2SO4-doped sample exhibited the lowest water contact angle.