Studies on the preparation and properties of conductive polymers. VII. Use of two-stage method to prepare Ag–Hg alloy on polymer films

Polymer metal chelate films were prepared by silver nitrate mixed with polymers containing functional groups such as poly(vinyl alcohol) (PVA) by using two-stage method to prepare Ag–Hg alloy on polymer films. In the first stage, polymer silver chelate was treated with doping agents. In the second stage, these treated films were further treated with Hg metal. After the two stage treatment, films with good electrical conductivity can be obtained. © 1994 John Wiley & Sons, Inc.     

X-ray analysis of α-, β-, and γ-phase Ag–Hg alloy films produced on polymer substrates by casting polyacrylamide–AgNO3 aqueous solution in Hg atmosphere

It is reported that, by dropping Hg metal on the wet α-phase Ag–Hg alloy film formed on the cast polyacrylamide–AgNO₃ aqueous solution, the α phase of fcc structure can be converted into other phases that contain more Hg. The X-ray analysis of these phases reveals that they are the β phase of hexagonal structure and the γ phase of bcc structure. It is also shown that the lattice constant of the α phase can be controlled to some extent by pH of the aqueous solution of PAAm from which the alloy film is formed.     

Joining of sintered silicon carbide using ternary Ag–Cu–Ti active brazing alloy

Sintered silicon carbide was brazed to itself by Ag–35.25 wt%Cu–1.75 wt%Ti filler alloy at 860 °C, 900 °C and 940 °C for 10 min, 30 min and 60 min. Mechanical properties both at room temperature and high temperature were measured by flexural strength. The interfacial microstructure was investigated by electron probe microanalysis (EPMA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental results indicate that increased brazing temperature heightens the flexural strength and the maximal four-point flexural strength reaches 342 MPa at room temperature. In addition longer holding times result in thicker reaction layer, which increases mismatch of coefficients of thermal expansion (CTE) between SiC substrate and reaction layer and finally leads to poor mechanical properties due to high residual stresses. High temperature flexural strength decreases with an increase of test temperature due to softening of the filler alloy. A reaction layer composed of TiC and Ti₅Si₃ was observed at the interface of SiC/filler alloy and there is a representative microstructure: SiC/continuous fine TiC layer/discontinuous coarse Ti₅Si₃ layer/filler alloy.     

Electrochemical corrosion study of Sn–3Ag–3Cu solder alloy in NaCl solution

The corrosion behaviour of Sn–3Ag–3Cu (at%) alloy was investigated in 0.1 M NaCl solution by potentiodynamic polarization and impedance spectroscopy measurements and compared with that of the Sn–3Ag–0.5Cu (at%) solder employed in the packaging of some microelectronic components and devices. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to characterize the samples prior to and after the electrochemical tests. Results showed that in NaCl solution the corrosion resistance of the Sn–3Ag–3Cu alloy was better than that of the Sn–3Ag–0.5Cu solder. The presence of tin oxychlorides or oxyhydroxychlorides was detected at the surface of both alloys investigated after the electrochemical tests. The better corrosion behaviour of the Sn–3Ag–3Cu alloy compared to the Sn–3Ag–0.5Cu solder can be ascribed to a more adherent and compact corrosion products layer.     

Preparation and physical properties of konjac glucomannan–polyacrylamide blend films

The blend films of konjac glucomannan (KGM) and polyacrylamide (PAAm) were prepared by using the solvent‐casting technique. Transparent blend films were obtained in all blending ratios. The physical properties of the films were investigated by Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and by measurement of mechanical properties. The results indicated the occurrence of intra‐ and intermolecular interactions of the pure components, as well as the intermolecular interactions between KGM and PAAm through hydrogen bond formation. The thermal stability and mechanical properties of both tensile strength and elongation at break of the films were improved by blending KGM with PAAm. It was worth noting that the blend film had the greatest tensile strength when the KGM content in the blend films was around 30 wt %. Surface morphology of the films observed by SEM was consistent with the above‐noted results. Furthermore, the water absorbability of the blend films was also investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 882–888, 2001     

One-stage method of preparing core–shell particles

A one-stage method of preparing code–shell particles was developed for the system containing silicone oils and glycidle methacrylate (GMA). Although the formation of core–shell particles for the systems containing silicone oils and methyl methacrylate (MMA) or styrene (ST) is possible in view of thermodynamics, the core–shell particles were not obtained. Factors such as better compatibility of silicone oils with vinyl monomers, higher swelling degree of silicone rubber in the vinyl monomers, and larger addition rate of thevinyl monomers with Si—H during the crosslinking of silicone oil containing vinyl group and Si—H (SVB and SHB) do not favor the formation of core–shell particles. X-ray photoelectron spectrometer (ESCA) was used in determining the formation of core–shell particles. The mechanism of the formation of core–shell particles is discussed. © 1995 John Wiley & Sons, Inc.     

Synthesis of silicon–substituted azonitriles and their use in preparing caulks

A silicon-substituted azonitrile, has been synthesized by the hydrosilation of 5-hexene-2-one azine with methyldichlorosilane in the presence of chloroplatinic acid, followed by hydrocyanation with anhydrous HCN, and subsequent oxidation with chlorine. The azonitrile is an initiator for radical polymerizations. It is especially useful for the preparation of low molecular weight polymers that, after treatment with acetic anhydride, cure at room temperature in the presence of atmospheric moisture. The preparation of a series of room temperature- vulcanizable materials based on a tetrafluoroethylene/methyl vinyl ether copolymer is described.     

Fabrication of Ag–SnO2 Contact Materials from Gas‐Atomized Ag–Sn Powder Using Combined Oxidation and Ball‐Milling Process

Silver–tin oxide (Ag–SnO₂) is considered to be an effective alternative to silver–cadmium oxide (Ag–CdO), which is carcinogenic and, therefore, toxic to the human body. In this study, Ag–SnO₂ powder was prepared through a combined oxidation and ball‐milling process using gas‐atomized Ag–Sn powder. During oxidation, the Ag₃Sn phase disappeared at 800°C and SnO₂ was formed without Ag oxidation; this SnO₂ formed a layer structure that covered the Ag matrix. The thickness of the oxide layer increased after the composite was subjected to a second oxidation process. Owing to the resultant core (Ag)‐shell (SnO₂) structure, the electrical conductivity of the fabricated composite was considerably lower than that of commercially available materials. However, the electrical conductivity increased remarkably after ball milling of the samples, which allowed the SnO₂ surface layer to be peeled off and crushed. Following high‐pressure magnetic pulsed compaction, the SnO₂ was found to be homogeneously distributed in the Ag matrix, which exhibited a lamellar structure.     

Effect of polymerization method on structure and properties of cationic polyacrylamide

Acrylamide and 2‐(methacryloyloxy)ethyltrimethylammonium chloride (AM/MADQUAT) copolymers were synthesized by solution and inverse microemulsion polymerization using (NH₄)₂S₂O₈/NaHSO₃ as redox initiator at the same feed mole ratio, and their microstructure, such as sequence distribution and composition distribution, was calculated from monomer reactivity ratios of different polymerization methods. The results show that charge distribution is more uniform for copolymer prepared in inverse microemulsion than that in solution, and copolymer composition distribution is close to unity, and maintains approximately at the feed ratio. Furthermore, the influence of the two structures of cationic polyacrylamides on kaolinite floc size and effective floc density, reduction of Zeta potential and floc compressive yield stress had been investigated at pH 7. The results show that the kaolinite floc size and effective floc density are strongly dependent upon copolymer microstructure, with greater floc size and lower effective floc density being observed for copolymer prepared in inverse microemulsion than for that in solution. Copolymer microstructure has a marked effect on the Zeta potential, whose reduction in the magnitude was much greater in the presence of copolymer prepared in inverse microemulsion than that in solution. Greater compressive yield stress was achieved for the strong flocs produced by copolymer prepared in inverse microemulsion than for the weak flocs produced by that in solution. The difference in flocs compressive yield stress may be attributed to flocs structure. Therefore, in this article, a correlation between the cationic polyacrylamide structure and flocculation property for kaolinite suspension was established. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Catalyst characterization and activity of Ag–Mn complex oxides

High diastereoselectivities were obtained in the heterogeneous catalytic hydrogenation of a chiral pyrrole derivative with complete conversion, in non-acidic medium. The effects of catalytic metals, temperature and solvents on the conversion and the diastereomeric excess (d.e.) were investigated. In the hydrogenation of N-(1′-methylpyrrole-2′-acetyl)-(S)-proline methyl ester over rhodium on carbon, in methanol, at 20 bar and room temperature (RT) the highest d.e. was 95%. This is a successful example of a diastereoselection in the saturation of pyrrole ring.     

Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity

Ag–TiO₂ multiphase nanocomposite thin films were prepared on quartz substrates by the liquid phase deposition (LPD) method from a mixed aqueous solution of ammonium hexafluouotitanate, silver nitrate and boric acid under ambient temperature and atmosphere followed by calcination at 500 °C for 1 h. The grain growth of anatase was depressed upon Ag⁺ doping. However, silver ions not only promoted (or catalyzed) the formation of brookite phase but also reduced the phase transformation temperature of anatase to rutile. With increasing AgNO₃ concentration, the transmittance and band gap of the composite thin films decreased; however, the intensity of surface plasmon absorption (SPA) peaks increased and their peak position shifted to a longer wavelength range. When AgNO₃ concentration was higher than 0.03 M, the prepared samples consisted of anatase, brookite, rutile and metal silver nanocrystal particles, and their grain size ranges were 5–30 nm. The photocatalytic activity of the Ag–TiO₂ multiphase nanocrystal composite thin films prepared by this method exceeded that of pure TiO₂ thin films by a factor of more than 6.3 when AgNO₃ concentration was kept in the range of 0.03–0.05. This was attributed to the fact that there were many hetero-junctions, such as anatase/rutile, anatase/brookite, Ag/anatase, Ag/rutile and so on, existed in the Ag–TiO₂ multiphase nanocomposite films.     

La–Ag–Co perovskites for the catalytic flameless combustion of methane

Ag represents an interesting dopant for the highly active LaCoO₃ perovskites used for the catalytic flameless combustion (CFC) of methane, due to its ability to adsorb and activate oxygen and to the possibility of incorporation into the framework as Ag⁺ or Ag²⁺, with formation of oxygen vacancies. In the present work we compared the catalytic activity and resistance to sulphur poisoning of a series of LaCoO₃, x%Ag/LaCoO₃, La_1−xAg_xCoO₃ samples (nominal composition), the latter two notations indicating post-synthesis Ag loading or direct incorporation during the synthesis, respectively. The samples were prepared by flame pyrolysis (FP) and by the sol–gel (SG) method, leading to different particle size and possibly to different incorporation degree of the dopant, quantified by Rietveld refinement of XRD patterns.Higher activity was observed, in general, with fresh catalysts synthesised by FP. The SG samples demonstrated a slightly better resistance to sulphur poisoning when considering the conversion decrease between the fresh and the poisoned samples, due to lower surface exposure. However, interesting data have been obtained with some of the Ag-doped poisoned FP samples, performing even better than the fresh SG-prepared ones.Ag addition led to a complex change of activity and resistance to poisoning. The activity of FP-prepared samples doped with a small amount of Ag (e.g. 5 mol%) was indeed lower than that of the undoped LaCoO₃. By contrast, a further increase of Ag concentration led to increasing catalytic activity, mainly when big extraframework Ag particles were present. By contrast, for SG samples a low Ag amount was beneficial for activity, due to an increased reducibility of Co³⁺.     

Sol‐gel preparation and properties of Ag‐containing bioactive glass films on titanium

Ag‐containing bioactive glass films (Ag/Ca atomic ratios of 0, 5% and 10%) were sol‐gel prepared for bioactive and antibacterial modification of titanium. The gel powders calcined at 610°C are mainly amorphous confirmed by x‐ray diffraction, but small diffraction peaks of Ca₃SiO₅ and silver are detected. The film surface is porous with the pore size of ~200 nm. Silver‐rich sub‐micro particles with sizes of 100‐480 nm are present at the surface of Ag‐glass films. CaP phase, metallic silver and silica are detected by x‐ray photoelectron spectroscopy. The mean apparent bonding strength of the films is as high as 21±1 MPa measured by the pull‐off test. The potentiodynamic polarization test shows that the coated samples have better corrosion resistance than the polished sample. The Ag‐glass coatings and their wafer samples exhibit antibacterial activity against S. aureus. The coated samples are covered by apatite layer after soaked in the simulated body fluid for 2 weeks, demonstrating their bioactivity.     

Discovery of the bi-layered structure in spin-coated polyacrylamide films on the gold surface

The reflection-absorption Fourier transform infrared spectroscopy (RA-FTIR) with the polarized lights was used to characterize polyacrylamide (PAL) films spin-coated on the gold (Au) surfaces. The PAL films spin-coated on the Au surface show the characteristics of a bi-layered structure. The first layer attached to the Au surface with a thickness of around 70 nm shows no chain orientation due to the dewetting effect of the Au surface. The upper layer is composed of the PAL molecules oriented parallel to the Au surface as the film thickness increases, which is believed to be due to the spin-coating effect. The bottom and the top layers are optically isotropic and anisotropic, respectively, as confirmed by the analysis of the RA-FTIR spectra. The thickness-threshold is of the order of the end-to-end distance (R_ee, 67 nm) of PAL molecules (M_w ∼ 10⁶) indicating the dewetting distance through which the Au surface functions.     

Novel hydrogels of PVP–CMC and their swelling effect on viscoelastic properties

Polyvinylpyrrolidone (PVP) and carboxymethyl cellulose (CMC) mixed hydrogels were prepared by heat treatment. The physical characteristics of the hydrogels were studied by Fourier transform infrared spectroscopy and scanning electron microscopy. The swelling study of the hydrogels in water shows remarkable water absorption property. The swelling effect on the rheological behavior of PVP‐, PVP–CMC‐, and CMC‐based hydrogels was investigated to judge its application on uneven surface of body. The rheological properties (storage modulus, loss modulus, and complex viscosity) of samples before drying and swelled (15, 30, and 60 min) were measured against angular frequency and composition. The hydrogel containing PVP/CMC ratio of 20 : 80 appeared to be the best hydrogel from rheological and water absorbent points of view. These properties and low cost of the materials utilized in this work suggest that this hydrogel is a viable alternative product for dressing materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Antibacterial activity and antistatic composites of polyester/Ag‐SiO2 prepared by a sol–gel method

Poly(butylene adipate‐co‐terephthalate) (PBAT) composites containing silver‐silica (Ag‐SiO₂) were prepared using an in‐situ sol–gel process. Maleic anhydride‐grafted PBAT (PBAT‐g‐MA) and multihydroxyl‐functionalized Ag‐SiO₂ were used to improve the compatibility and dispersibility of Ag‐SiO₂ within the PBAT matrix. The composites were characterized morphologically using transmission electron microscopy and chemically using Fourier transform infrared spectrometry. The existence of Ag‐SiO₂ nanoparticles on the substrate was confirmed by the ultraviolet–visible absorption spectra. The antibacterial and antistatic properties of the composites were evaluated whether SiO₂ enhanced the electrical conductivity was tested as well as whether Ag enhanced the antibacterial activity of the PBAT‐g‐MA/SiO₂ or PBAT/SiO₂ composites. The PBAT‐g‐MA/SiO₂ or PBAT/SiO₂ composite that contained Ag had better antibacterial activity (more than 1.3‐fold). The functionalized PBAT‐g‐MA/Ag‐SiO₂ composite can markedly enhanced antibacterial and antistatic properties due to the carboxyl groups of maleic anhydride, which acted as coordination sites for the Ag‐SiO₂ phase, allowing the formation of stronger chemical bonds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrochemical behavior of the Ti–6Al–4V alloy coated with a-C:H films

In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the I_D/I_G ratio). Potentiodynamic corrosion tests in 0.5 mol l⁻¹ NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential (E_corr) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l⁻¹ aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance (R_ct) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces.     

The effect of phase separation on the structure and permeability of gelatin–dextran films

The effect of polymer–polymer phase separation on the transport properties of gelatin–dextran films has been studied. In the gelatin–dextran–water system, the phase separation and gel formation do not occur due to the presence of a nonsolvent, but depend entirely on the temperature and the total polymer concentration. It has been found that the permeability of polymer blend films to aqueous solutes can be varied not only by changing the volume ratio of the phases, but also by varying the size of the individual domains of the two phases in the films. Under the conditions of restricted demixing (e.g., after gel formation), the course of the phase separation process can be changed by varying the length of time allowed for unrestricted separation. The two most important parameters affecting the result are the total polymer concentration in the casting solution, and the temperature regime. An exponential dependence of the permeation coefficient on the volume fraction of the solvent in the film is shown.     

A novel method for preparing composites of PDMS/PS core–shell emulsion and polystyrene

A novel and simple method for preparing composites of PDMS/PS core–shell emulsion and polystyrene was reported. This method was based on emulsion and suspension in situ polymerization. The relationship between the process of core–shell emulsion breaking and electrolyte concentration was studied by spectrophotometry. The results of transmission electron microscopy showed that polydimethylsiloxane soft particles were dispersed uniformly in the composites. Diameters of the composite beads ranged from 0.5 to 4.0 mm, which could be controlled by adjusting the amount of hydroxyapatite. At last, the properties of the latex film including water absorption ratio, contact angle, pendulum hardness and transparency were tested. The results showed that the content of emulsion obvious affected the properties. During the process of emulsion and suspension in situ polymerization, the contact angle of the latex films ascended to 106.06° and the transmission ratio at 500 nm decreased to 0.3 with the increasing of core–shell emulsion. Whereas, the absorption and pendulum hardness fell to 0.37% and 322 S, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Characterization of electropolymerized graphite fiber–polyacrylamide composites

The synthesis of a series of graphite fiber-polyacrylamide composites was performed electrochemically in dilute sulfuric acid (0.125M)-acrylamide (2M) solution, 1 : 1 sulfuric acid (0.25M) : acetone-acrylamide (2M) solution, and 1 : 1 sulfuric acid (0.25M) : 2-propanol-acrylamide (2M) solution, respectively, using graphite fiber bundles as the working electrode. The graphite fiber-polyacrylamide composites, synthesized in a 1 : 1 2-propanol : sulfuric acid-acrylamide solution, were more easily characterized than those synthesized from the sulfuric acid-acrylamide solution that contained no alcohol. Composites that were synthesized in a dilute sulfuric acid solution were, however, more readily crosslinked. (Fourier transform infrared spectroscopy, FTIR, confirmed the formation of inter-chain and intrachain imide functional groups after the resin was cured at ≈ 200°C.) Polymer weight gain analysis, coupled with surface morphology studies using scanning electron microscopy, showed that the thickness of the coatings, and hence the volume fraction of the resin in the composites, varied linearly with the time of electropolymerization. Scanning electron microscopy revealed an open and folded chain surface structure, which permitted unrestricted permeation of the monomer onto the electrode surface. Differential scanning calorimetry of the electropolymerized resins confirmed a glass transition temperature of between 180 and 207°C. © 1994 John Wiley & Sons, Inc.