Plasma polymerization and deposition of glycidyl methacrylate on Si(100) surface for adhesion improvement with polyimide

Thin polymer films were deposited on Si(100) surfaces by plasma polymerization of glycidyl methacrylate (GMA) under different glow discharge conditions. The FT‐IR, X‐ray photoelectron spectroscopy (XPS), and amine treatment results suggested that the epoxide functional groups of the deposited films had been preserved to various extents, depending on the plasma deposition conditions. The use of a low radio frequency power (～ 5 W) and a relatively high system pressure (100–400 Pa) readily resulted in the deposition of thin films having nearly the same composition of the epoxide functional groups as that of the GMA homopolymer. The plasma‐polymerized GMA (PP‐GMA) thin films deposited on the Ar plasma‐pretreated Si(100) surfaces were retained to a large extent after acetone extraction, suggesting the presence of covalent bonding between the PP‐GMA layer and the Si surface. Thermal imidization of the poly(amic acid) precursor of polyimide on the GMA plasma‐polymerized Si(100) surface resulted in a strongly adhered polyimide film. The adhesion results further suggested that the GMA polymer had been grafted on the Si(100) surface and the epoxide functional groups had undergone reactive interaction (curing) with the carboxylic and amine groups of the poly(amic acid) during thermal imidization. Copyright © 2001 John Wiley & Sons, Ltd.     

Intrinsic redox states of polyaniline studied by high-resolution X-ray photoelectron spectroscopy

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. Received: 16 May 2000/Accepted: 29 August 2000     

XPS studies of charge transfer interactions in some polyphenylacetylene-electron acceptor systems

X-ray photoelectron spectroscopy (XPS) studies have been performed on charge transfer complexes of trans-polyphenylacetylene (PPA). The acceptors used included halogens, such as I₂ and Br₂, and organic electron acceptors, such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), chloranil, fluoranil, and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ). Incomplete and relatively weak charge transfer interactions were observed in most of the complexes. These help to account for the relatively low conductivity levels observed in most of the PPA complexes when compared with the corresponding complexes of other conjugated polymers. PPA has also been found to interact with molecular oxygen to some extent in solution. In complexes involving O₂, Br₂, and fluoranil, XPS data suggest that the charge transfer interaction may have proceeded further than the pure formation of molecular charge transfer complexes.     

Preparation of Nanosized Metallic Particles in Polyaniline

The preparation of nanosized gold and palladium particles in polyaniline has been carried out via the reduction of AuCl(3) or Pd(NO(3))(2) by polyaniline in either aqueous media or N-methylpyrrolidinone (NMP). When the reduction of AuCl(3) was carried out in NMP solutions of polyaniline, the Au particles were on the order of 20 nm. The reduction of AuCl(3) or Pd(NO(3))(2) by polyaniline in the powder form in aqueous media resulted in the accumulation of the elemental Au or Pd on the surface of the polyaniline particles. Subsequent dissolution of the polyaniline in NMP resulted in metal particles of about 50 to 200 nm being dispersed in the NMP solution of polyaniline. The rate of metal salt reduction and the size of the metal particles were found to be strongly dependent on the medium used, the initial ratio of metal ions to polyaniline, and the reaction time. The polyaniline-metal particle systems were characterized using X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy, and FTIR spectroscopy. Scanning and transmission electron microscopy and laser light scattering were used to determine the size of the metal particles in polyaniline. Copyright 2001 Academic Press.     

Polymerization and oxidation of pyrrole by organic electron acceptors

Simultaneous chemical polymerization and oxidation of pyrrole have been initiated by organic electron acceptors, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetrachloro-o-benzoquinone(chloranil). The polypyrrole (PPY) complexes so produced are semiconductive and granular in nature. For the PPY–DDQ and PPY–chloranil complexes obtained from bulk polymerization, the respective electrical conductivities (σ) are of the order of 10^?1 and 10^?3 ohm^?1 cm^?1. However, σ is substantially lower for the complexes prepared in solvent media. Both complexes are relatively stable in the atmosphere. Thin uniform films of the PPY–organic acceptor complexes have also been synthesized on SnO₂ electrode by electrochemical polymerization in acetonitrile. The physicochemical properties of the PPY–organic acceptor complexes prepared chemically under the various experimental conditions are examined in detail.     

Synthesis and characterization of electrically conducting polyaniline–TCNE complexes

Polyaniline–tetracyanoethylene (TCNE) complexes can be synthesized either from emeraldine base or emeraldine hydrochloride by a relatively simple method. The complexes demonstrate greater stability than the emeraldine hydrochloride at elevated temperatures and under high current densities. The electrical conductivity of the complexes synthesized from emeraldine base can be varied from < 10^?6 to 0.2 S/cm by varying the amount of TCNE incorporated. The complexes synthesized from emeraldine hydrochloride are slightly more conductive than the starting emeraldine hydrochloride. In both types of complexes, it appears that electron transfer between the polyaniline and TCNE has occurred resulting in the formation of some positively charged polyaniline nitrogen and TCNE anions.     

Electroless Deposition of Copper on Poly(tetrafluoroethylene) Films Modified by Plasma-Induced Surface Grafting of Poly(4-vinylpyridine)

Argon plasma-pretreated poly(tetrafluoroethylene) (PTFE) films were solution coated with a thin layer of poly(4-vinyl pyridine) (P4VP). Subsequent exposure of the films to argon plasma resulted in the grafting of P4VP on the PTFE films. Electroless plating of copper could be carried out effectively on the P4VP-grafted PTFE (P4VP-g-PTFE) surface after PdCl₂ activation and in the absence of SnCl₂ sensitization (the Sn-free process). The catalytic processes of the electroless plating of copper in the presence and absence of sensitization by SnCl₂ were also compared. The effect of glow discharge conditions on the P4VP concentration and the adhesion strength of the electrolessly deposited copper was investigated. The T-peel adhesion strength of the electrolessly deposited copper with the graft-modified PTFE film was improved in the absence of SnCl₂ sensitization and could reach about 3 N/cm. PdCl₂ activation and electroless deposition of copper could not be carried out on the pristine or the Ar plasma-treated PTFE surface in the absence of prior sensitization by SnCl₂. X-ray photoelectron spectroscopic (XPS) analysis revealed that the electrolessly deposited copper delaminated from the P4VP-g-PTFE film by cohesive failure inside the PTFE film.     

Surface structures of fluoropolymer,polyolefin and polyester films after modification by graft polymerization

Pristine and argon plasma pretreated polytetrafluoroethylene (PTFE), polystyrene (PS), high-density polyethylene (HDPE) and poly(ethylene terrephthalate) (PET) films have been subjected to near-UV light-induced graft polymerization with water-soluble acrylamide (AAm), the sodium salt of styrene sulfonic acid (NaSS), acrylic acid (AAc) and N,N-dimethylaminoethylmethylacrylate (DMAEMA) monomers. The structure and composition at the substrate surface with grafted polymer were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). In most cases, the density of surface grafting is enhanced by plasma pretreatment. For each polymer substrate with a substantial amount of grafting, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This stratified microstructure is consistent with the static secondary ion mass spectroscopy (SIMS) and Ar⁺ beam depth profiling results. The two latter techniques also suggest that when the grafted polymer has a bulky substituent, there is less efficient penetration of the grafted polymer below the surface.     

Plasma protein adsorption and thrombus formation on surface functionalized polypyrrole with and without electrical stimulation

A surface modification technique was developed in which heparin was covalently immobilized onto electrically conductive polypyrrole (PPY) film through poly(ethylene glycol) methacrylate (PEGMA) graft copolymerization and subsequent cyanuric chloride activation. In vitro plasma protein adsorption and thrombus formation experiments were carried out on the various films. The PEGMA-graft-copolymerized PPY surfaces with immobilized heparin have good bioactivity indicated by low level of protein adsorption, high ratio of albumin to fibrinogen adsorption, and low thrombus formation, making them potentially good candidates for biomedical applications. Since the PPY film retained significant electrical conductivity after surface modification, the effect of electrical stimulation on protein adsorption and thrombus formation was also evaluated. The covalently immobilized heparin on the PPY film was able to retain its bioactivity after 4 days of immersion in PBS. The film after long-term immersion in PBS also retained sufficient electrical conductivity for electrical stimulation still to be effective for reducing protein adsorption.     

Probing the interaction between peptides and metal oxides using point mutants of a TiO2-binding peptide

An increasing number of peptides with specific binding affinity to inorganic materials are being isolated using combinatorial peptide libraries without prior knowledge about the interaction between peptides and target materials. The lack of understanding of the mechanism and the contribution of constituent amino acids to the peptides' inorganic-binding ability poses an obstacle to optimizing and tuning of the binding affinity of peptides to inorganic materials and thus hinders the practical application of these peptides. Using the phage surface display technique, we previously identified a disulfide-bond-constrained peptide (-CHKKPSKSC-, STB1) cognitive of TiO2. In the present study, the interaction of STB1 with TiO2 was probed using a series of point mutants of STB1 displayed on phage surfaces. Their binding affinity was measured using a quartz crystal microbalance with energy dissipation measurement and compared on the basis of the delta f or delta D values. The three K residues of STB1 were found to be essential and sufficient for phage particle binding to TiO2. One mutant with five K residues showed not stronger but weaker binding affinity than STB1 due to its conformational restriction, as illustrated by molecular dynamics simulation, to align five K residues in a way conducive to their simultaneous interaction with the TiO2 surface. The contextual influence of noncharged residues on STB1's binding affinity was also investigated. Our results may provide insight into the electrostatic interaction between peptides and inorganic surfaces.