Surface modification of halogenated polymers. 6. Graft copolymerization of poly(tetrafluoroethylene) surfaces by polyacrylic acid

Polyacrylic acid can be grafted onto polytetrafluoroethylene (PTFE) once the latter has been reduced locally by an electrode. Two reduction treatments are performed either by direct contact of an electrode or by scanning electrochemical microscopy (SECM) leading to disc shaped reduced zones of, respectively, ∼1 mm and ∼100 μm diameter. Deactivation of reduced PTFE zones by air or oxidant exposure yields unsaturations on the polymeric surface that are prone to graft copolymerization. The grafted polymer, polyacrylic acid, is a cation exchanger that can complex to a fluorescent and reducible cation such as toluidine blue. Desorption of the cation from the polymeric film is characterized using UV-visible, fluorescence spectroscopies and also SECM. The latter technique is used to study the desorption kinetics, which is interpreted by a model taking into account the slow diffusion of the cation inside the membrane. The mean thickness of the film, which is initially ∼100 nm is about the same after one year of air exposure, which emphasizes the stability of the film with time.     

重氮盐用于无机材料的表面改性研究进展

重氮盐的表面改性是一种新型有效的表面改性方法,可实现对无机、有机、生物材料的改性。综述了重氮盐用于无机材料表面改性的特点及方法,如电化学还原、氧化还原、UV辐照接枝、热化学反应、机械接枝、超声波和微波辅助改性,并重点介绍了近年利用重氮盐对碳纳米管、石墨、玻璃碳、金属、半导体、石英和纳米金刚石等无机材料的表面改性及应用。     

Surface grafting polymerization and modification on poly(tetrafluoroethylene) films by means of ozone treatment

Surface modification on polytetrafluoroethylene (PTFE) films was performed with sequential hydrogen plasma/ozone treatments and surface-initiated polymerization. C-H groups were introduced to the surface of PTFE films through defluorination and hydrogenation reactions under hydrogen plasma treatment. The C-H groups then served as ozone accessible sites to form peroxide groups under ozone treatment. Grafting polymerization initiating from the peroxide groups was performed on the PTFE film surface with using acrylamide, acrylic acid, glycidyl methacrylate and 2-(2-bromoisobutyryloxy)ethyl acrylate (BIEA) as monomers. With utilizing the isobutylbromide groups on the surface of PTFE-g-PBIEA film as initiators, sodium 4-styrenesulfonate (NaSS) was polymerized onto the PTFE film surface via atom transfer radical polymerization, to bring arborescent macromolecular structure to PTFE film surface. The chemical structures of the macromolecules on PTFE film surfaces were characterized with FTIR-ATR, SEM-EDX and XPS. The surface hydrophilicities of modified PTFE films were significantly enhanced with the modification.     

Surface modification of poly(tetrafluoroethylene) film by chemical etching,plasma, and ion beam treatments

Chemical etching, plasma, and ion beam treatments were used to modify the surface of Polytetrafluoroethylene (PTFE). Each surface treatment method developed different surface characteristics. In addition to morphological observation, contact angle, atomic chemical composition, and adhesion strength were measured after treatment with various methods. The different adhesion strengths were explained based on the morphology and atomic chemical composition of the treated PTFE surfaces. The chemical etching showed substantial defluorination, and the adhesion strength was fairly high. The argon plasma treatment introduced very large amounts of oxygen into the surface, and the surface was very smooth with a crater‐like structure. Ion beam treatment induced a form of spires whose dimensions were of several micrometers, depending on the ion dose, whereas the oxygen plasma‐treated samples showed short spires with spherical particles on the top. The spire‐like surface morphology and increased surface area during bonding by ion beam treatment appear to be the reason for a higher adhesion strength than that of the oxygen plasma‐treated PTFE. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1913–1920, 2000     

远程等离子体处理对聚四氟乙烯表面的功能化改性

采用远程氩等离子体对聚四氟乙烯(PTFE)膜进行了表面改性研究,通过接触角测定仪、扫描电子显微镜(SEM)和X射线光电子能谱仪(XPS)等手段,分析研究了改性后材料表面结构、性能的变化。结果表明:PTFE表面经远程氩等离子体处理后,表面微观形态和表面化学成分均发生了变化,且处理效果优于常规氩等离子体。远程氩等离子体可以在一定程度上抑制电子、离子的刻蚀作用,强化自由基反应,使材料表面获得更好的改性效果。经远程氩等离子体短时间(100s)处理后,PTFE表面的F/C比例从1.97降至1.44,O/C比例从0.015增至0.086;表面的水接触角从108°减小到53°;表面自由能从22.4×10-5N·cm-1增加至52.3×10-5N·cm-1。     

Hybrid coating on steel: ZnNi electrodeposition and surface modification with organothiols and diazonium salts

Sacrificial electrodeposited ZnNi is currently studied for replacing chromate conversion coatings (CCC) in anticorrosion applications. The present-day performances of ZnNi are still away from those of CCCs and the additional organic layers such as polymers and paints are still permeable and cannot prevent the corrosive species to reach the metal. Suitable adhesion primers could improve the situation by minimizing the access of the corrosive species to the polymer/metal interface.As a contribution to this interface problem, the present work provides a comparison of the protective properties of two structurally related molecules (4-nitrothiophenol and 4-nitrobenzenediazonium) grafted on a ZnNi coating electrodeposited on steel. Films of 4-nitrophenyl have been prepared according to the self-assembly process while films of 4-nitrobenzene have been obtained by electrochemical grafting, n-dodecanethiol being used as model system.The adsorption of these molecules as well as the resulting organic film is characterized by X-ray photoelectron spectroscopy (XPS) and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The protective properties of the organic films against corrosion are investigated by linear sweep voltammetry (LSV), cyclic voltammetry (CV) and scanning vibrating electrode technique (SVET).     

重氮盐静电自组装的研究与应用

综述了重氮盐静电自组装反应的特点,重点介绍了重氮盐与几种负离子如羧基、磺酸基、氧负离子和磷酸根之间发生自组装反应的研究情况,以及近几年来重氮盐静电自组装技术在碳纳米管、C60、石英、金属这些无机材料表面改性上的应用。     

Covalent attachment of pyridine-type molecules to glassy carbon surfaces by electrochemical reduction of in situ generated diazonium salts. Formation of ruthenium complexes on ligand-modified surfaces

In this study, pyridine, quinoline and phenanthroline molecules were covalently bonded to glassy carbon (GC) electrode surfaces for the first time using the diazonium modification method. Then, the complexation ability of the modified films with ruthenium metal cations was investigated. The derivatization of GC surfaces with heteroaromatic molecules was achieved by electrochemical reduction of the corresponding in situ generated diazonium salts. X-ray photoelectron spectroscopy (XPS) was used to confirm the attachment of heteroaromatic molecules to the GC surfaces and to determine the surface concentration of the films. The barrier properties of the modified GC electrodes were studied in the presence of redox probes such as Fe(CN)₆³⁻ and Ru(NH₃)₆³⁺ by cyclic voltammetry. Additionally, the presence of the resulting organometallic films on the surfaces was verified by XPS after the chemical transformation of the characterized ligand films to the ruthenium complex films. The electrochemical behavior of these films in acetonitrile solution was investigated using voltammetric methods, and the surface coverage of the organometallic films was determined from the reversible metal-based Ru(II)/Ru(III) oxidation waves.     

Ageing of plasma-treated poly(tetrafluoroethylene) surfaces

Highly hydrophobic poly(tetrafluoroethylene) (PTFE) surfaces were modified with an air glow discharge plasma to improve their wettability. However, the hydrophilic character obtained diminishes with time, due to molecular movement in the polymer. We have determined that the ageing process is strongly affected by the environment and temperature in which the surfaces are stored. A hydrophobic environment and high temperatures promote faster recovery of the original properties of PTFE than low temperatures. Nonetheless, a hydrophilic environment, even at high temperatures, prevents the surface from losing the polar character obtained from the plasma treatment, stopping the ageing process. Moreover, this process is reversible since the character of the treated surface changes when the environment changes (i.e. from water to air). The hydrophilicity of the surfaces was evaluated by contact angle measurements of a droplet of water.     

Surface modification of poly(tetrafluoroethylene) films by graft copolymerization for adhesion enhancement with electrolessly deposited copper

The surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) films via UV-induced graft copolymerization with either 3-(trimethoxysilyl)propyl methacrylate (TM-SPMA) or glycidyl methacrylate (GMA) was carried out to enhance their adhesion to electrolessly deposited copper. The surface compositions of the PTFE films at various stages of surface modification and electroless plating were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the graft-copolymerized PTFE film to the electrolessly deposited copper was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment time after graft copolymerization, and the extent of thermal post-treatment after metallization. The maximum T-peel strength achieved between the electrolessly deposited copper and the GMA graft-copolymerized PTFE film was about 11 N/cm. This adhesion strength represented a more than 20-fold increase over what could be achieved when the PTFE film was treated by Ar plasma alone. The mechanisms of the adhesion strength enhancement and the failure mode in the metal-polymer laminates were also investigated. It was found that the failure was cohesive in nature within the PTFE film.     

Surface modification of poly(tetrafluoroethylene) film by plasma graft polymerization of sodium vinylsulfonate

Poly(tetrafluoroethylene) (PTFE) surface was modified by the graft polymerization of sodium vinylsulfonate, and the chemical composition of the graft-polymerized PTFE surface was analyzed by X-ray photoelectron spectroscopy. Peroxides were formed on the PTFE surface by a combination procedure of argon plasma irradiation and air exposure, and the graft polymerization of sodium vinylsulfonate was initiated by the peroxide groups at 65–80°C. The peroxide concentration is 3 × 10⁺¹³ to 5 × 10⁺¹³ numbers/cm². The average degree of polymerization of the graft polymers was 3.4 × 10³. The graft polymer is distributed over the PTFE surface, but part of the PTFE surface remains uncovered. The coverage with the graft polymer is 43%. The PTFE surface graft polymerized with sodium vinylsulfonate was somewhat hydrophilic, but the hydrophilicity was lower than that of the PTFE surface modified by plasma treatment. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 77–84, 1997     

The properties of poly(tetrafluoroethylene) (PTFE) in tension

Samples of DuPont 7A and 7C Teflon (PTFE, poly(tetrafluoroethylene)) were tested in tension at strain-rates between 2×10⁻⁴ and 0.1 s⁻¹ and temperatures between −50 and 150 °C. Additionally, using a Hopkinson bar, a temperature series was undertaken in tension between −50 and 23 °C at a strain rate of 800 s⁻¹. To investigate the small-strain response, strain gauges were used to measure axial and transverse strain allowing the Poisson ratio to be calculated. The effect of crystallinity was investigated using 7C material thermally processed to produce more amorphous material. As expected, the tensile mechanical properties of PTFE are significantly affected by strain-rate and temperature, but only to a limited extent by crystallinity. The Poisson ratio at small strains was found to differ in tension (≈0.36) and compression (≈0.46). Failure behavior and microstructure were correlated to temperature induced phase transitions.     

Surface modification of poly(tetrafluoroethylene) films by plasma polymerization and UV-induced graft copolymerization for adhesion enhancement with electrolessly-deposited copper

Surface modification of H₂ plasma-pretreated poly(tetrafluoroethylene) (PTFE) films, either by plasma polymerization and deposition of GMA, or by UV-induced graft copolymerization with glycidyl methacrylate (GMA), was carried out for adhesion enhancement with the electrolesslydeposited copper. XPS and FTIR results revealed that the epoxide groups in the plasma-polymerized GMA (pp-GMA) layer had been preserved to various extents, depending on the glow discharge conditions. The T-peel adhesion test results showed that the adhesion strengths of the electrolesslydeposited copper on both the pp-GMA modified PTFE (pp-GMA-PTFE) film and the GMA graftcopolymerized PTFE (GMA-g-PTFE) film were much higher than that of the electrolessly-deposited copper on the pristine or the H₂ plasma-treated PTFE film. The high adhesion strength between the electrolessly-deposited copper and the surface-modified PTFE film was attributed to the fact that the plasma-polymerized and the UV graft-copolymerized GMA chains were covalently tethered on the H₂ plasma-pretreated PTFE surface, as well as the fact that these GMA chains were spatially and interactively distributed into the copper matrix.     

Modification of poly(tetrafluoroethylene) and copper foil surfaces by graft polymerization for adhesion improvement

Thermal graft polymerization-induced lamination of surface-modified copper foil to surface-modified poly(tetrafluoroethylene) (PTFE) film was achieved in the presence of an epoxy resin adhesive and glycidyl methacrylate (GMA) monomer, or in the presence of GMA and hexamethylenediamine (HEDA). The copper foil surfaces were pretreated with an organosilane coupling agent (SCA), such as (3-mercaptopropyl)trimethoxysiane, 3-(trimethoxysilyl)propyl methacrylate, or N¹-[3-(trimethoxysilyl)propyl]diethylene-triamine. The silanized copper foils were subjected to brief Ar plasma treatment and subsequently to UV-induced graft polymerization with GMA (the Cu-SCA-g-GMA surface). Surface modification of PTFE film included Ar plasma treatment alone, or Ar plasma pretreatment followed by UV-induced graft polymerization with GMA (the GMA-g-PTFE surface). The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. The Cu-SCA-g-GMA/epoxy resin-GMA/PTFE or Cu-SCA-g-GMA/GMA–HEDA/GMA-g-PTFE laminates exhibited T-peel adhesion strengths in excess of 9 N/cm and the joints delaminated by cohesive failure inside the bulk of the PTFE film. The strong adhesion in these Cu foil-PTFE laminates is attributable to the fact that the GMA chains are covalently tethered on both the PTFE and the silanized Cu surfaces, as well the fact that these grafted GMA chains are covalently incorporated into the highly crosslinked network structure of the adhesive at the interphase.     

Voltammetric quantification of the spontaneous chemical modification of carbon black by diazonium coupling

Surface coverage limits obtained through the spontaneous and reductive reaction of 1-diazo-anthraquinone ions with Vulcan XC72 carbon black have been studied using cyclic voltammetry. The effect of modifying the surface structure of the carbon, varying reaction conditions and time, and the use of sequential reactions were studied. The maximum loading of AQ that could be obtained was 1.0 × 10⁻⁴ mol g⁻¹, consisting in the best case of a 3:1 ratio of covalently bound to adsorbed species. Based on literature specific area values for the carbons and measured specific capacitances, it is concluded that only ca. 25% of the BET area of the pristine Vulcan XC72 is accessible to the diazonium ions, and that a loosely packed monolayer of bound and adsorbed species is formed on this accessible area. Carboxylic acid groups on the carbon surface were not found to limit the total loading of AQ, but did significantly favor covalent bonding over adsorption.     

Argon plasma treatment-induced grafting of acrylic acid onto expanded poly(tetrafluoroethylene) membranes

Expanded poly(tetrafluoroethylene) (ePTFE) is used in facial reconstruction surgery. For some specific applications ePTFE is required to interface with the underlying bone. However, ePTFE is classified as bioinert thus limiting integration at the bone-tissue interface. The incorporation of functional groups onto the ePTFE surface was carried out in the current study using argon plasma treatment-induced grafting of acrylic acid (AA) to improve integration. High surface coverage (grafting extent from XPS of up to 90%) was achieved and resulted in high hydrophilicity and high water uptake (up to 470% of the grafted PAA mass). The contribution of species present in the plasma to the incorporation of functional groups onto the ePTFE surface was evaluated with charged species observed to play an equally important role to neutral species in this study. The effects of sample position in the plasma chamber as well as the effect of grafting parameters (plasma power, monomer concentration, and reaction time) on the grafting outcome were evaluated. The mechanical properties of the AA grafted membranes under tensile, compression and nanoindentation were evaluated.     

Characterisation of amine functionalised poly(3-hydroxybuturate-co-3-hydroxyvalerate) surfaces

There is an increasing acceptance of the importance of tailoring biomaterial surface properties. This study aimed to introduce and characterise amine functionalities onto the hydrophobic bacterial polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Gamma irradiation induced simultaneous grafting of 2-aminoethyl methacrylate (AEMA) onto PHBV films was carried out using various concentrations of AEMA (2.5 or 4.5 w/v%) in either water or methanol and at two irradiation doses (4.5 or 9 kGy). Successful grafting was verified from XPS analysis, water contact angle and ATR-FTIR spectroscopy. Characterisation using DSC indicated that grafting had occurred predominantly in the amorphous region of the PHBV substrate. ¹H NMR of the grafting solution post grafting showed that monomer conversion is incomplete in methanol. The use of gold nano-particles (AuNPs) as a simple tool to probe the presence of these functional groups was evaluated using a suspension of citrate functionalized AuNPs prepared by reduction of Au(III) with citric acid. These particles were found to be polydisperse (0.8-2 nm and 7-70 nm) and negatively charged (zeta potential of −33 ± 9 mV) and capable of interacting electrostatically with the amine groups on the PHBV surface and imaged using SEM.     

Grafted polymers from poly(4-vinylpyridinium) salts

4-Vinyl pyridine can be added via its vinylic double bond to the quaternary nitrogen atom of poly(4-vinylpyridinium chloride). When this reaction is carried out successively, model grafted polymers with grafts of a constant length with a known number of electric charges, have been obtained. Potentiometric measurements, infra-red and ¹H n.m.r. spectroscopic studies confirm the structure of the polymers.     

Adhesion of copper to poly(tetrafluoroethylene) surfaces modified with vacuum UV radiation from helium arc plasma

Poly(tetrafluoroethylene) (PTFE) film surfaces were exposed to vacuum UV (VUV) radiation from He dc arc plasmas that were made to rotate inside a graphite tube by the application of an auxiliary magnetic field. The films were covered with optical filters having different cutoff wavelengths to vary the VUV radiation that modified the fluoropolymer surface. Photo-etching was detected, as well as surface modification that showed the following: (1) water contact angles decreasing with wavelengths of 173 nm or shorter; (2) surface roughening; (3) defluorination of the surface and formation of cross-linking bonds in the top 10 nm of the surface as detected by XPS analysis; and (4) incorporation of oxygen upon exposure to air. An improvement in the adhesion of copper to these modified surfaces was observed.     

Surface modification of poly(ethylene terephthalate) fiber by excimer light

Changes in the surface topography and chemical structure on the surfaces of poly(ethylene terephthalate) (PET) fibers and films caused by the irradiation using an excimer laser beam and excimer lamp light were monitored. The SEM (scanning electron microscopy) observation suggests that a wavy shape was produced by irradiation with the excimer laser beam, while such a wavy shape was not observed when the excimer lamp light was used. The XPS (X-ray photoelectron spectroscopy) analysis of the fiber surface suggests that the O/C intensity ratio was reduced by irradiation using the laser beam, whereas this ratio gradually increased with irradiation with the lamp light. This difference is attributed to the difference in the number of photons in the laser beam, which was much higher than that in the lamp light, although the laser beam and lamp light had the same wavelength and energy. As for wettability to water, the contact angle was smallest for PET irradiated by the excimer lamp light. For adhesion studies, the PET fabric was first coated with an epoxy acrylate solution, irradiated with excimer light, dipped into RFL (resorcinol-formaldehyde-latex) adhesive, and the peel strength to rubber sheet was examined. When the irradiation by the excimer laser beam was compared with that with the excimer lamp light, the laser irradiation showed a good adhesion property even for rubber vulcanization carried out for a long time at high temperature.