Aniline was found to polymerize slowly and spontaneously on the platinum and palladium metal surfaces in an aqueous acid solution of the monomer. The phenomenon was thus equivalent to an “electroless polymerization” process. The polyaniline (PANI) so-deposited were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The chemical state of the electroless deposited PANI film was near to that of the 75% intrinsically oxidized nigraniline (NA) state of PANI. The electrolessly deposited PANI films exhibited similar protonation–deprotonation behavior as that of the aniline homopolymer. The amount of the PANI deposited on the metal surface was affected by the monomer concentration, the nature of the acid medium, and the oxygen content in the reaction medium.

High-resolution X-ray photoelectron spectroscopic (XPS) measurements of the various intrinsic redox states of polyaniline (PANI), using a monochromatized Al—Kα source, were carried out. The presence of the imine, amine and positively charged nitrogen species corresponding to a particular intrinsic redox state and protonation level of the polymer was resolved quantitatively and unambiguously. The result confirmed the peak assignments of former XPS core-level studies using the lower resolution non-monochromatized Mg—Kα X-ray source. Thus, the high-resolution XPS using a monochromatized Al—Kα X-ray source is a truly unique tool for the convenient and quantitative analysis of the various intrinsic redox states of PANI.

Chemical modification of the argon plasma-pretreated Si(100) surface by UV-induced surface graft polymerization with either glycidyl methacrylate (GMA) or glycidyl acrylate (GA) was carried out. The GA graft polymerized Si substrate was further subjected to coupling reaction with aniline (An) and finally oxidative graft polymerization of An. The composition and microstructure of the graft-polymerized Si(100) surfaces were studied by X-ray photoelectron spectroscopy (XPS) and imaging XPS, respectively. The graft concentrations of the GMA polymer, GA polymer, and An polymer increased with increasing concentration of the respective monomer used for graft polymerization. The graft polymerization efficiency of GA on the Ar plasma-pretreated Si(100) was much higher than that of GMA. Ethanol, when used as a solvent, catalyzed the coupling reaction elf the epoxide groups of GA with An and should be of more than 40 vol % in concentration to achieve the optimum effect. The protonation-deprotonation characteristics, interconvertible intrinsic redox states, and metal reduction behavior of the polyaniline (PANI) chains, obtained from subsequent oxidative graft polymerization of An on the modified Si(100) surface, were grossly similar to those of the PANI homopolymer. The resistance of the modified Si(100) surface from consecutive graft, polymerization with GA and An was on the order of 10(7) Omega /sq.

Invertase was covalently immobilized on the emeraldine (EM) base form of polyaniline (PAN) films and powders with surface-grafted acrylic acid (AAc) polymer. The immobilization proceeded via the amide linkage formation between the amino groups of invertase and the carboxyl groups of the grafted AAc polymer chains on EM in the presence of a water-soluble carbodiimide. The surface structure and composition of the grafted–modified and enzyme-functionalized EM base were characterized by X-ray photoelectron spectroscopy (XPS). It was found that the amount of immobilized invertase increased linearly with the concentration of surface-grafted AAc polymer chains. EM powders could be graft-modified and enzyme-functionalized more effectively than EM films. The decrease in activity of the immobilized invertase was considered to be due to, among other factors, the reduced accessibility of substrate molecules to the active sites of the enzyme and the conformational change of the invertase molecules as a result of the covalent immobilization. However, the immobilized enzyme was less sensitive to temperature deactivation below the optimum temperature as compared to that of the free form. The optimum pH value of invertase was not affected by the immobilization reaction, but the pH stability range was broadened. The immobilized invertase also exhibited a significantly improved stability during storage in buffer solution over that of the free enzyme.

Chemical modification of emeraldine (EM) based powders via thermally induced surface graft copolymerization with acrylic acid (AAc), 4-styrenesulfonic acid (SSAc) and amphoteric N,N′-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS) was carried out in aqueous media. The effects of temperature on graft copolymerization and Mohr's salt on homopolymerization were also studied. The chemical composition and structure of the graft-copolymerized powders were studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. In all cases, the graft yield increased with the monomer concentration and the temperature used for graft copolymerization. Certain Mohr's salts effectively inhibited the production of the homopolymers. Graft copolymerization with AAc and SSAc readily gave rise to self-protonated and semi-conductive EM powders, with the conductivity increasing with the extent of grafting. However, steric hindrance and spatial configuration of the grafted chains had substantially limited the extent of protonation of the EM substrate by the protonic acid functional groups of these chains.