Role of unsaturated groups in glow discharge polymerization

The role of unsaturated groups of the starting compounds in glow discharge polymerization was investigated by elemental analysis, infrared spectroscopy, and ESCA. Tetramethylsilane (TMS), trimethylvinylsilane (TMVS), and ethyltrimethylsilane (ETMS) were used as starting materials. Glow discharge conditions (W/FM value meaning the rf power input per mass of the monomers) as well as a degree of the unsaturation of the starting materials had strong influences upon the polymer deposition rate and the elemental composition of the formed polymers. The C_1s and the Si_2p spectra showed that the chemical composition of these polymers was distinguished by either presence or absence of the unsaturated groups in the starting compounds rather than kind of the unsaturated groups. The polymer formation, when the monomers containing double and triple bonds were served, is proceeded not only through these unsaturated bonds but also through the cleavage between Si and C atoms.     

Glow discharge polymerization of trimethylvinylsilane and tetramethylsilane

Glow discharge polymerizations of trimethylvinylsilane (TMVS) and tetramethylsilane (TMS) were compared. Vinyl groups in TMVS slightly contribute the polymer-formation process only when glow discharge polymerization was performed at the W/FM parameter less than 500 MJ/kg. Elemental compositions of the polymers prepared from TMVS, which are rich in carbon content, shows strong dependence on operational conditions, the W/FM parameter; but the polymers from TMVS consist of the almost same chemical structures as those from TMS. Slight differences between the starting materials in chemical structure does not reflect on bulk properties of the formed polymers but on surface properties such as surface energy and adhesion.     

Plasma polymerization of tetrafluoroethylene. I. Inductive radio frequency discharge

The plasma polymerization of tetrafluoroethylene in an inductively coupled radio frequency glow discharge, using a flow system, was studied. A simple long tube reactor, with the coupling coil placed at the middle of the tube and gas entrance and exit at the respective ends, was used. Deposition rates and the chemical nature of the polymer (as revealed by ESCA spectra and surface energy studies) are obtained as a function of location in the reactor tube with respect to the coupling coil and of applied energy per unit mass of tetrafluoroethylene (W/FM). It was found that a fluorinepoor polymer, containing considerable carbon–oxygen bonds (after contact with air), is obtained at all locations at high W/FM. When a low W/FM is utilized, such a fluorine-poor polymer is also obtained at locations downstream from the coupling coil (the location of the highest energy density) in the reactor. In the latter case a fluorine-rich polymer containing very little oxygen is formed upstream from the coil. The polymer deposition rate distribution is also considerably broader in a high W/FM plasma than when low W/FM is used. These results are in agreement with earlier studies indicating that fluorine abstraction and decomposition due to fluorine etching occur when the energy density, as expressed by W/FM, is high.     

Deposition of polymethyl methacrylate on polypropylene substrates using an atmospheric pressure dielectric barrier discharge

In this work, an atmospheric pressure glow-like dielectric barrier discharge in helium with small admixtures of methyl methacrylate (MMA) is used for the deposition of thin polymethyl methacrylate (PMMA) films. The effect of discharge power and feed composition (monomer concentration) on film properties has been investigated by means of Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results are described by defining a W/FM value, where W is the discharge power, F the monomer flow rate and M is the molecular weight of the monomer. It is shown in this paper, that the deposition rate and the chemical composition of the deposited film change with varying W/FM values. At low W/FM values, high deposition rates of up to 2 nm/s are observed and the plasma-polymerized MMA chemically resembles the conventionally synthesized PMMA. In contrast, using high W/FM values (≥102 MJ/kg) leads to lower deposition rates (as low as 0.9 nm/s), while the plasma-polymerized MMA films contain less ester groups and a larger amount of ether and/or alcohol groups. One should therefore carefully choose the deposition parameters in order to obtain a high deposition rate and a high retention of ester groups in the plasma-polymerized MMA films.     

Surface modification of polyethylene and magnetite powders by combination of fluidization and plasma polymerization

A new surface modification process of powders was attempted, using the combination of fluidization and plasma polymerization techniques. This study shows that the combination of the fluidization and plasma polymerization techniques is useful in the surface modification of powders. Polyethylene and magnetite powders were first fluidized, and then were modified in the fluidization state by the plasma polymers of tetrafluoroethylene (TFE). XPS spectra of the modified powders showed that the surfaces of the polyethylene and magnetite powders were coated with fluorine-containing polymers, and that the polymers were mainly composed of CH, CF, and CF₂ groups. The elemental composition (F/C atomic ratio) and the composition of the fluorinated carbons in the plasma polymers were dependent on the W/FM parameter, as well as the TFE concentration in the TFE/Ar mixture. It is emphasized that the W/FM parameter is a factor used to control the chemistry of the plasma polymerization reactions. The triboelectric charge of the magnetite powders, when modified by the plasma polymerization of the TFE/AR mixtures, was higher than the usnmodified by about two. The static electrification properties of the powders can changed by the plasma-polymer-coating. © 1993 John Wiley & Sons, Inc.     

Coatings and surface modification by methane plasma polymerization

Polymers formed from plasma-polymerized methane were employed to modify the surface properties of silicone rubber membrane. Polymers were evaluated based on the energy input parameter W/FM, where W is the discharge power, F is the monomer flow rate, and M is the molecular weight of the monomer. Dealing with the characteristics of plasma polymerization and the deposited polymer film, the effect of pumping rate on deposition rate and the coating thickness, surface energy, and gas permeabilities of methane-plasma-polymer-coated silicone rubber membrane were investigated in three plasma regions. Because more reactive species are expelled at high pumping rates, the monomer-deficient region is reached at lower W/FM in the high pumping rate system than that in the low pumping rate system. The composite parameter W/FM had a strong influence on coating thickness, gas permeability, surface energy, and the polar component of the surface energy but little effect on its dispersion component. Examination of gas permeabilities indicated that coating thickness was another important controlling factor on the properties of plasma polymer.     

Introduction of amino functionalities on ethylene-co-tetrafluoroethylene film surfaces by NH3 plasmas

In order to form active sites for grafting amino groups, a predominant elimination of fluorine atoms from fluoropolymers such as poly(tetrafluoroethylene), ethylene-co-tetrafluoroethylene co-polymer (ETFE) and poly(vinylidene fluoride) was carried out using the plasma irradiation technique, and the possibility that amino functional groups could be formed on the fluoropolymer surfaces was investigated. The NH₃ plasma irradiation led to considerable elimination of fluorine atoms from the fluoropolymers, as well as grafting of nitrogen functionalities. The formation of nitrogen-containing groups was strongly influenced by the magnitude of the W/FM parameter, and the NH₃ plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable for the surface modification process. XPS spectra for the NH₃ plasma-modified surfaces showed that the NH₃ plasma attacked predominantly CF₂—CF₂ sequences rather than CH₂—CH₂ sequences in the ETFE polymer. The primary amino groups formed on the ETFE film surfaces were determined by fluorescence measurements. The concentration of the amino groups formed on the surfaces was not constant but varied according to the W/FM parameter. NH₃ plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable in grafting amino groups on the ETFE film surfaces.     

Pervaporation membranes for ethanol–water mixture prepared by plasma polymerization. III. Perfluorocarbon membranes

Pervaporation membranes for the ethanol–water mixture were prepared by plasma polymerization of tetrafluoroethylene, perfluoropropane, and perfluoropropylene onto porous substrates. The influence of the monomers on the elemental ratio (F/C) of the polymer depositions by X-ray photoelectron spectroscopy was rather small compared with that of the W/FM parameter (W = wattage for plasma excitation, FM = mass flow rate of a monomer). The optical emission spectroscopy indicated the similarity of gaseous species formed in the plasmas. The membranes were found ethanol-permselective, showing separation coefficients (α_EtOH) around 4–7 and a wide range of permeation rates (J), 10–10^?2 kg/m² h, for the 4.8 wt % ethanol solution at 40°C. The α_EtOH of the membranes with thicker depositions could be correlated to the F/C ratios as a measure of membrane hydrophobicity. It was thought that, by making a plot α_EtOH against J values for the perfluorocarbon membranes, they could be classified into three groups on thickness of deposition. The ethanol-separation mechanisms for each group, which may contain four kinds of mass transfer schemes, i.e., distillation through larger pores, flow of sorption layer at the liquid–membrane interface, and diffusions through deposition or substrate, were also discussed.     

Studies on plasma polymerization of hexamethyldisiloxane in the presence of different carrier gases

Plasma polymerization of hexamethyldisiloxane(HMDSO) in the presence of different carrier gases such as H₂, He, N₂, Ar, and O₂ was carried out using an inductively coupled electrodeless glow discharge. The polymerization kinetics showed that the monomer HMDSO plasma‐polymerized at different rates from low to high for the carrier gases H₂, He, N₂, Ar, and O₂ in that order. The products were studied using FTIR, electron spectroscopy for chemical analysis, and elemental analysis. The results indicated that HMDSO molecules underwent different degrees of fragmentation in plasma polymerization for different carrier gases and radio frequency (RF) powers. The polymer deposition rate and the structures of products were mainly dependent on molecular fragmentation, which varied with carrier gas and imposed RF power. O₂ and H₂ gases can incorporate in the plasma polymers to form products containing more oxygen or hydrogen components, while other gases such as N₂ have no detectable component in products. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1434–1438, 2001     

Plasma polymerization of organosilicon compounds

Plasma polymerizations in five silicon compounds having chemical formula of (CH₃)₃Si? X? Si(CH₃)₃, X = none, CH₂, NH, O, and S atoms, were investigated by elemental analysis, infrared spectroscopy, and ESCA. The chemical composition of polymers plasma-polymerized was influenced by the X groups in (CH₃)₃Si? X? Si(CH₃)₃. Polymers, when X was S atoms, possessed no sulfur; and X was CH₂ groups polymers rich in carbon and hydrogen atoms were formed. Details in chemical composition were discussed by IR and ESCA. Such differences in chemical composition reflected on gas permeability of the plasma films.     

Investigation of surface pre-treatments for the structural bonding of titanium

This paper evaluates wet-chemical pre-treatments (alkaline etching, anodising) and a plasma treatment for structural bonding of titanium (Ti₆Al₄V). The main objective of this study is the comparison of the applicability of the plasma pre-treatment to wet-chemical treatments on titanium for structural bonding. In this context, an atmospheric pressure plasma device was used to deposit thin functional films from hexamethyldisiloxane (HMDSO) precursor on titanium.X-ray photoelectron spectroscopy (XPS) was employed to assess the chemical composition of the surface after different pre-treatments on the titanium substrate, while the morphology and the film thickness were investigated with scanning electron microscopy (SEM). The adhesion properties on titanium were evaluated by means of a wedge test in hot/wet conditions. After bonding tests the fracture surface and the failure loci were analysed.Using a long arc plasma generator and HMDSO precursor almost stoichiometric SiO₂ coatings were obtained on the titanium substrate. These coatings exhibit good long-term durability and bond strength compared to an alkaline etching in the wedge test. The investigated anodising process leads to oxide layers revealing a highly porous nanostructure. In contrast to the alkaline etching, the plasma derived coatings and the oxide layer produced by the anodising process exhibit a higher micro, respectively nano roughness, and hence a better long-term durability.     

High-temperature elastomers: Glass transition–structure correlations for two systematic series of linear poly(carborane–siloxane)s. II. Incompatibility

Previously reported results related glass transition temperature to structure in two systematic series of poly(carborane–siloxane)s using a well-known copolymer composition–glass transition relationship 1/T_g = W₁/T_g1 + W₂/T_g2. The relationship was originally proposed to apply not only to copolymers, but also to diluent systems. Accordingly, mixtures of polymers within each series were prepared and the thermomechanical spectra were determined by the technique of torsional braid analysis. The binary mixtures included poly(dimethylsiloxane) with polymers in both series and a mixture of two ? CB₁₀H₁₀C? siloxane polymers. In all cases, the thermomechanical spectra revealed only those transition regions characteristic of the individual components. This type of behavior is indicative of phase separation of incompatible polymeric species.     

Etching Induced Stepped Nanostructure on Pb(Mg(1–x/2)Mn(x/2)W1/2)O3 Ceramics

A new solid solution system, Pb(Mg_(1–x/2)Mn_(x/2)W_1/2)O₃, is formed by replacing Mg²⁺ with Mn²⁺ in the Pb(Mg_1/2W_1/2)O₃ complex perovskite. The solid solution remains in the orthorhombic Pmcn symmetry up to x = 0.1. It is observed that for such a chemical modification, the surface of the grain changes significantly. A stepped surface nanostructure appears in the Mn‐substituted perovskite. Detailed surface morphology of the stepped patterns was revealed by atomic force microscopy (AFM), which determined that the interlayer step height varies from 2.3 to 8.3 nm. Analyse by XRD, SEM, EDX, and AFM suggest that the nature of the stepped surface structure may be the result of etching rather than spiral growth or two‐dimensional nucleation as it was previously believed.     

Deposition of HMDSO-based coatings on PET substrates using an atmospheric pressure dielectric barrier discharge

This paper presents results on the formation of coatings in an atmospheric pressure dielectric barrier discharge using hexamethyldisiloxane (HMDSO) as gaseous precursor. Plasma-polymerized films are deposited onto polyethylene terephthalate (PET) films using argon and argon/air mixtures as carrier gases. The chemical and physical properties of the obtained coatings are discussed in detail using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). FTIR and XPS results show that the composition of the gas phase and the chemical structure of the obtained coatings are clearly correlated. When pure argon is used as working gas, the film is polymeric with a structure close to [(CH₃)₂–Si–O]_n, which means that the deposited films resemble PDMS. However, if plasma-polymerization occurs in argon/air mixtures, the deposited film is silica-like containing only few carbon atoms. These dense SiO_x coatings generally exhibit high barrier properties, while pure HMDSO-derived films might be of importance for selective permeation. From this point of view, the capability of controlling the film composition by varying the operation conditions opens interesting perspectives.     

High-temperature elastomers: Glass transition–structure correlations for two systematic series of linear poly(carborane–siloxane)s. I

Nine linear poly(carborane–siloxane) high-temperature elastomers which differ systematically in chemical structure were investigated by torsional braid analysis. The structural variations include two different carborane cage structures in the polymer chain (? CB₁₀H₁₀C? and ? CB₅H₅C? ) and the stepwise increase in the number of ? Si(CH₃)₂? O? linkages associated with each cage in the repeat unit. Poly(dimethylsiloxane) was studied as the compositional limit of both series. The dynamic mechanical relaxations (at about 1 cps) of the materials are reported. These include the melting points of the semicrystalline polymers and the glass transitions and secondary transitions of all the polymers. The glass transition temperatures in each series were systematized using the well-known copolymer composition-versus-glass transition temperature relationship 1/T_g = W₁/T_g1 + W₂/T_g2.     

Electrostatic dissipation and flexibility of poly(oxyalkylene)amine segmented epoxy derivatives

A family of hydrophilic and flexible epoxy polymers was prepared from the reaction of poly(oxyalkylene)amines and diglycidyl ether of bisphenol‐A (DGEBA) at 1:1 molar ratio of N H to epoxide. The use of a high molecular weight (M_W = 1000–6000) poly(oxyethylene–oxypropylene)amine and a low M_W amine as curing agents provided epoxy materials with good properties in toughness and hydrophilicity. The hydrophilicity, probed by surface resistivity of these cured materials, was found to be affected by the nature and weight content of poly(oxyethylene) segment in the polymer backbone, and also by the degree of crystallinity. Specifically, in the presence of a water‐soluble poly(oxyethylene–oxypropylene)diamine of M_W 2000 the cured epoxies can reach surface resistivity as low as 10^8.6–9.6 Ω/□. In comparison, the water‐insoluble poly(oxypropylene)diamine of M_W 2000 afforded a higher surface resistivity of 10^10.5 Ω/□ because of the difference in hydrophilicity between oxyethylene and oxypropylene functionalities. Poly(oxypropylene)diamine of M_W 230 as the sole curing agent generated an epoxy with even higher surface resistivity of 10¹³ Ω/□ due to a highly crosslinking structure. With proper selection of mixed poly(oxyethylene–oxypropylene)diamine (25 wt%) and 2‐aminoethanol (9 wt%), the DGEBA cured polymer had an appropriate surface resistivity of 10^9.8 Ω/□ for antistatics. Moreover, this material was extremely ductile in appearance and showed over 500 % elongation at break during mechanical tests. The high flexibility is rationalized by the balanced chemical structure of poly(oxyalkylene) segments and bisphenol‐A distributed in a slightly crosslinked system. © 2000 Society of Chemical Industry     

Reversible and Irreversible Adhesion of Polymers: Possibilities for Measurement and Calculation

Comparative analysis of existing direct and indirect techniques for estimation of the work of adhesion (W_A ) between a polymer and a solid surface - inverse gas chromatography (IGC), wetting, direct adhesion forces measurement - has been carried out. The work of adhesion was calculated from experimental data obtained using different techniques for identical polymer/solid systems. The relationship between the work of adhesion and the bond strength was analyzed, including possible W_A estimations from destructive micromechanical tests. For non-polar polymers, whose adhesion is due to dispersion interaction only, all techniques are in good agreement with each other. However, the estimates of work of adhesion obtained by different techniques considerably differ for polar polymers. The reason for this obviously consists in deficiency of theoretical knowledge about non-dispersion interactions at interfaces. Each of the considered approaches has its own advantages and shortcomings. The problems concerning the estimation of non-dispersion component of the work of adhesion can be solved only by comprehensive use of several different techniques.     

Effect of Surface Tungstate W<Superscript>5+</Superscript> Species on the Metathesis Activity of W-Doped Spherical Silica Catalysts

The high surface area W-doped spherical silica (SSP) catalysts were prepared with different sequences of W and Si addition (W–Si_(Alt), Si₁–W_2, and W₁–Si₂) by the sol–gel method with CTAB as a structure directing agent and compared with the impregnated one (W/SSP). All the catalysts exhibited high specific surface area (～?1100 m² g^?1) with a closely perfect spherical shape. The presence of surface/sub-surface tungstate W⁵⁺ species, crystalline bulk WO₃, and tetrahedral tungsten oxide species on the prepared catalysts was investigated by means of X-ray photoelectron spectroscopy depth profile analysis, X-ray diffraction, and Raman spectroscopy. Without in situ reduction by the reactants/products, tungstate W⁵⁺ species was found on the top surface of the as-prepared W–Si_(Alt) whereas for the Si₁–W₂, W/SSP, and W₁–Si₂, the W⁵⁺ appeared only on the sub-surface of the catalysts after 5 and 15 s Ar⁺ etching. The abundance of surface W⁵⁺ species is suggested to facilitate the establishment of the active tungsten carbenes and was correlated well to the catalytic activity in propene metathesis. The surface W⁵⁺-activity relationship of the WO₃-based metathesis catalysts is useful especially when the catalyst activity did not depend solely on the amount of active tetrahedral coordinated tungsten oxides.     

Surface characterization of segmented siloxane–urethane block copolymers

New siloxane–urethane block copolymers were synthesized and the effect of a siloxane moiety on microphase segregation in soft/hard block copolymers was studied by several analytical methods. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) provided topographical and bulk composition information. Electron Spectroscopy for Chemical Analysis (ESCA) provided surface chemical information. Fourier Transform Infrared Spectroscopy (FTIR) provided chemical bond information for the near-surface region. Thermogravimetric Analysis (TGA) provided information concerning the thermal stability of the polymers. Differential Scanning Calorimetry (DSC) provided information on the soft and hard block segments within the polymer. These studies showed that the block copolymer contained and enhanced silicone-containing surface. For films cast on glass, less silicon was detected in the bulk (exposed by physically removing the surface material), and on the backside (glass) of the polymer film, than on the air-exposed surface. Of particular interest is the fact that data also show that the solvents, from which the polymers were cast, have a significant influence on microphase segregation. The films cast from THF have higher silicone concentrations at the surface as compared to polymers cast from DMAC/CH₂CL₂ or dioxane. © 1993 John Wiley & Sons, Inc.     

A 31P-NMR study of peroxo species formed during oxidation of cyclohexene with hydrogen peroxide in tri-n-butylphosphate catalyzed by heteropolyacids

In the oxidation of cyclohexene with H₂O₂in monophasic tri-n-butylphosphate (TBP) solution catalyzed by Keggin-type 12-heteropolyacids, i.e., H₃PMo_12-xW _x O₄₀(x=0–12), several peroxo species were observed by ³¹P-NMR spectroscopy in lower field than the original heteropolyacids. Their composition varied regularly with that of the starting catalyst. The P-containing peroxo species formed was deduced as [PM₄O₈(O₂)₈]^3-(M = Mo, W). The peroxo species formed more easily with a decrease in the W content, x of H₃PMo_12-xW_xO₄₀. It was further indicated from the reactivity with cyclohexene and the comparison with catalytic performance that W-rich peroxo species were catalytically more active than Mo-rich peroxo species for the oxidation of cyclohexene in this reaction system.