Oxidative chemical copolymerization of pyrrole(Py) and aniline (An) by copper perchlorate in acetonitrile was carried out. By varying the monomer feed ratios, the copolymer compositions could be effectively modified. The high-resolution X-ray photoelectron spectroscopy (XPS) analysis using monochromatized Al Kα X-ray source enabled the quantification of the proportions of pyrrole and aniline units in the copolymers. The copolymer composition and microstructure obtained were also characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and electrical conductivity measurements. The results of XPS, FTIR, SEM and conductivity measurements supported the presence of copolymers consisting of random segments of aniline and pyrrole units. The copolymers generally exhibited reduced electrical conductivity, compared to those of the respective homopolymers, probably as a result of the interruption of the polaron lattice by the presence of the second monomer.

The interactions of thermally evaporated potassium atoms with poly(p-phenylene vinylene) (PPV) and its soluble derivative, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was studied in situ by angle-resolved X-ray photoelectron spectroscopy (XPS). The changes in the C 1s core-level line shape of the polymers, the evolution of the K 2p core-level spectra, and the changes in chemical compositions at the interface with progressive deposition of the metal atoms were carefully monitored. The interactions of the K atoms with the conjugated polymer surfaces were compared with those involving metals of other work functions. Diffusion of the K atoms into the polymers and distinct charge transfer interactions were observed at the interface. The migration of bulk adsorbed oxygen to the surfaces of both polymers during the K deposition process resulted in an increase in oxygen concentration at the K/polymer interfaces. The diffusion of the adsorbed oxygen from the bulk of the conjugated polymer film played a dominant role in the interfacial reactions. The interfacial layer contains mainly oxidized metal and metal-polymer charge transfer species.

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.

Electroless plating of copper on poly(tetrafluoroethylene) (PTFE) films modified by NH3 plasma treatment and surface graft copolymerization with aniline had been carried out. For the electroless plating of copper, the polyaniline (PANI)-grafted PTFE (PANI-g-PTFE) surface, with the PANI in its fully reduced leucoemeraldine form, was activated directly in the Pd(NO3)(2) acid solution in the absence of prior sensitization by SnCl2. The compositions and chemical states of the PTFE surfaces during each stage of the surface modification, surface activation, and electroless deposition processes were studied by x-ray photoelectron spectroscopy (XPS). The adhesion strength of the electroless deposited copper on the PANI-g-PTFE surface exhibited a strong dependence on the graft concentration of PANI. A T-peel adhesion strength of about 5 N/cm was achieved for the electrolessly deposited Cu on the PANI-g-PTFE surface (the Cu/PANI-g-PTFE assembly). The high adhesion strength of the Cu/PANI-g-PTFE assembly was attributed to the synergistic effects of strong interactions between the grafted aniline polymer and the metal (including Pd) atoms, the spatial distribution of the PANI chains in the metal matrix, and the fact that the polyaniline chains were covalently tethered on the PTFE surface. XPS results also revealed that the Cu/PANI-g-PTFE assemblies delaminated by cohesive failure inside the PTFE film. (C) 2001 American Vacuum Society.

The effect of γ-ray irradiation on the emeraldine (EM) base form of polyaniline was investigated. The processes of γ-ray, UV, and thermally-induced graft copolymerization of EM base with acrylic acid (AAc) in a number of solvents and co-solvents were compared in an attempt to prepare a water-soluble EM through N-acylation. The presence of N-acylation was investigated by thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). In all cases, the graft concentration and the resulting surface conductivity were shown to be a function of the monomer concentration. The thermostability and weight loss behavior of the graft-copolymerized EM included those that were characteristic of the EM base, the AAc polymer and the amide polymer. Some of the graft-modified EM base samples exhibited good water solubility. In particular, the γ-ray-induced graft copolymerization of EM with AAc in N-methyl-2-pyrrolidinone(NMP)/water co-solvent readily gave rise to a water-soluble, self-protonated and semi-conductive EM, which could be cast into free-standing films from an aqueous solution.

Angle-resolved X-ray photoelectron spectroscopy was employed for the in situ study of the interactions between thermally evaporated copper atoms and conjugated electroluminescent polymer, such as poly(p-phenylene vinylene) and its soluble derivative, poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). Quantitative changes in the C1s and Cu2p core-level spectra, the CuLMM Auger line shapes, and the chemical stoichiometries of polymer–metal interfaces with progressive deposition of the copper atoms were carefully monitored. Chemical interactions had occurred between each polymer and the copper atoms, resulting in the formation of an interfacial layer of metal complexes. There appeared to be no significant migration of bulk absorbed oxygen to the polymer surface upon copper deposition unlike that observed during the deposition of metals of lower work function. Diffusion of Cu atoms into the near-surface region of the polymer was observed for PPV and MEH-PPV films. The interactions of the Cu atoms with the polymer surfaces were also compared with the results obtained for the Al/PPV and Al/MEH-PPV interfaces.

X-ray photoelectron spectroscopy (XPS) was employed for the study of the physicochemical interactions at electrode/polymer interfaces involving metals of high and low work functions and thin films of poly(p-phenylene vinylene) (PPV) and poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene] vinylene (MEH-PPV), The changes in the C Is core-level line shape of the polymers, the evolution of the metal core-level spectra and the changes in chemical compositions at the interfaces involving polymer coated on indium-tin oxide (ITO), sputtered ITO on polymer, and in situ evaporated magnesium (Mg) on polymer were carefully monitored. Indium of the ITO in both the ITO/polymer and polymer/ITO assemblies was found to diffuse towards the polymer at the interface. Oxygen migration was also observed at the ITO/polymer interfaces, The results obtained from in situ analysis by angle-resolved XPS of the interactions between thermally evaporated Mg and PPV and Mg and MEH-PPV indicated the formation of an interfacial layer in each case. The surface diffusion of adsorbed oxygen from the bulk of the conjugated polymer film played a dominant role in the interfacial reactions. The interfacial layer consisted of Mg oxides, Mg clusters, Mg metal and Mg-polymer complexes. Copyright (C) 2000 John Wiley & Sons, Ltd.

X-ray photoelectron spectroscopy was employed for the in situ study of interactions between thermally evaporated Mg atoms and electroactive polyaniline (PANI) films of various intrinsic oxidation states. Quantitative changes in the N1s core-level spectra and the Mg2p core-level spectra, as well as the changes in surface chemical stoichiometry of these films throughout the Mg evaporation process were carefully monitored. Although the nitrogen sites appeared to be more attractive to the in-coming Mg atoms and the emeraldine base (EB) and nigraniline base (NA) films underwent an apparent decrease in intrinsic oxidation state ([=N-]/[-NH-] ratio) as a result of Mg evaporation, there is no direct interaction between the two species. On the other hand, the adsorbed oxygen from the bulk of the polymer film played a dominant role in the interfacial interactions between the polymer and the metal. Characterization of the delaminated indium-tin-oxide (ITO) and polymer surfaces from EB film and its camphorsulfonic acid-doped counterpart cast on ITO substrates had also been carried out to evaluate the interaction of PANI with the high work function metal.

Electroless plating of copper on polyaniline (PANI) films of different intrinsic oxidation states, viz., the emeraldine base (EB), the nigraniline (NA) and the leucoemeraldine (LM) states, in the complete absence of surface sensitization by SnCl2 was explored. The process consisted of two steps. The first step involved electroless deposition of palladium on PANI film in Pd(NO3)2 nitric acid solution. The Pd-laden films were subsequently used for the electroless plating of copper. It was found that electroless deposition of Pd and Cu occurred efficiently only on the fully reduced LM film surface. X-ray photoelectron spectroscopy was employed for the characterization of surface compositions and chemical states of the polymer films and the metals during the two electroless deposition processes. The quantitative changes in N1s core-level spectra and the evolution of Pd 3d and Cu 2p core-level spectra on the polymer films during the two-step process were carefully monitored. In Pd(NO3)2 nitric acid solution, all three types of the PANI films were protonated. Nevertheless, coupled Pd reduction occurred only on the LM film surface. The metallic Pd atoms on the LM film surface initiated the subsequent electroless plating of copper. The reduction of Cu(II) ions to Cu metal proceeded via the Cu(I) state. The effect of [Pd]/[N] mole ratio of the Pd-laden LM film on the rate of electroless plating of copper was also investigated.

The stability of the soluble, electroluminescent polymer, poly(2-methoxy-5-(2′-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) to photolysis, heat treatment, plasma and X-ray exposure was monitored by UV–VIS spectroscopy, Fourier transform infrared (FT–IR) spectroscopy and angle resolved X-ray photoelectron spectroscopy (XPS). Samples were either neat films of MEH-PPV or solutions of MEH-PPV in xylene. A significant broadening of the absorption spectrum with considerable blue shift and a rapid loss in photoluminescence intensity were observed when the polymer film and solution were illuminated with UV-visible light, or even with light of wavelength greater than 500 nm, in ambient air. Negligible change in effective conjugation length was observed when the polymer film was illuminated under an argon atmosphere with light of wavelength greater than 290 nm. The surfaces of MEH-PPV films were modified using argon, nitrogen and oxygen plasma. The formation of new functional groups on the polymer film surface was monitored by angle resolved XPS. The polymer film also lacks long-term stability when exposed to a moderate temperature of 160°C in ambient atmosphere, and suffers a considerable loss in effective conjugation. Finally, the loss in the effective conjugation length of the polymer film during X-ray exposure under ultra-high-vacuum environment is associated with the crosslinking of the polymer chains.

The surface microhardness of conventional thermoplastics lie between 0.1 and 0.6 GPa. The as-cast emeraldine (EM-25) base film of polyaniline (PANi) exhibits a surface microhardness of about 1 GPa. The hardness is increased to about 4 GPa in the highly cross-linked EM (EM-150) film. This hardness value 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 through protonation or through reduction to the leucoemeraldine state. Surface modification of the EM-150 films via graft copolymerization with acrylic acid or styrenesulfonic acid readily gives rise to hard-surfaced PANi films having microhardness values approaching 20 GPa. This surface hardness is comparable to many of those reported for the very hard-surfaced conventional polymers 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 charge-transfer interaction between the graft and the substrate chains.

Simultaneous lamination of emeraldine base (EB) films of polyaniline (PANI) was achieved during thermally induced surface graft copolymerization with various monomers, such as N,N′-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS), sodium salt of styrenesulfonic acid (NaSS), 1-vinyl imidazole (VIDz) and acrylic acid (AAc). The simultaneous thermal grafting and lamination process can be carried out under atmospheric conditions, and in the complete absence of an added polymerization initiator and surface preactivation of the EB substrates. The structure and chemical composition of the graft copolymerized surfaces from the self-delaminated junction in water were investigated by X-ray photoelectron spectroscopy (XPS). The effects of monomer concentration, thermal grafting/lamination temperature, and the physicochemical attributes of the various monomers on the observed lamination strength were studied. The efficiency of surface graft copolymerization and the lamination strength were found to increase with increasing temperature in the temperature range of 80–120°C. Maximum lap shear adhesion strengths of greater than 350N/cm2 and exceeding the yield strength of the substrate EB film could be readily achieved for grafting/lamination carried out in the presence of DMAPS, VIDz and AAc monomer.

The results obtained from the in situ analysis by angle resolved x-ray photoelectron spectroscopy (XPS) of the interactions between thermally evaporated metals (aluminum and indium) and conjugated electroluminescent polymer films, such as poly(p-phenylene vinylene) and its soluble derivative, poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), are reported. The changes in the carbon and metal core-level spectra and the chemical stoichiometries of polymer–metal interfaces with progressive deposition of the metal atoms were monitored. The interactions of the Al and In atoms with the polymer surfaces were compared. For both metals, a simple electrical contact was not formed. From the XPS studies, it was deduced that chemical reactions had occurred between the polymer and the metal, leading to the formation of an interfacial layer of metal oxides and complexes. The interfacial reactions were promoted by the surface oxidation states of the polymer, the migration of bulk adsorbed oxygen to the polymer surface upon metal deposition, and also in the case of MEH-PPV, by the oxygen from the alkoxy side chains.

The hardnesses of conventional thermoplastics lie between 0.1–0.6 GPa. The as-cast emeraldine base (EB) exhibits a surface microhardness of 1–2 GPa. The hardness is increased to 6 GPa in highly crosslinked EB (x-EB) film and can be further enhanced to about 8 GPa through protonation or through reduction. Surface modification of x-EB films via graft copolymerization with acrylic acid and styrenesulfonic acid readily gives rise to a semi-conductive, super-hard surface, having a micro-hardness of about 20 GPa. This surface hardness is higher than many of known super-hard-surfaced conventional polymers from high-energy ion-beam bombardments.

Adhesion of emeraldine base (EB) films of polyaniline (PANI) to plasma-pretreated polytetrafluoroethylene (PTFE) films and to copper foils were achieved via thermally induced surface graft copolymerization with concurrent lamination. The process was carried out under atmospheric conditions in the presence of pure and aqueous solutions of 1-vinyl imidazole (VIDz) or acrylic acid (AAc) and in the absence of an added polymerization initiator. The chemical composition and microstructure of the graft copolymerized surfaces from the self-delaminated junction in water and from the mechanically delaminated interfaces were investigated by X-ray photoelectron spectroscopy (XPS). The effects of monomer concentration and thermal grafting/lamination temperature on the observed lamination strength were studied for both the EB/PTFE and EB/Cu interfaces. The lap shear adhesion strength of the EB/PTFE junction also depended on the plasma pretreatment time of the PTFE surface. Maximum lap shear adhesion strength approaching 200 N/cm2 was obtained for the EB/PTFE interface laminated at 140°C for 1h in the presence of pure AAc monomer and with 40s of Ar plasma pretreatment time for the PTFE surface. A maximum lap shear adhesion strength of about 640 N/cm2 could be readily achieved for the EB/Cu interface for grafting/lamination carried out in the presence of 25vol% aqueous VIDz solution at 130°C.