Dielectric and microwave absorption properties of TiAlCo ceramic fabricated by atmospheric plasma spraying

Composite TiAlCo powders (TiO₂, Co₃O₄ and Al₂O₃) were synthesized by spray–drying technology. The phase composition and morphology of synthesized powders were characterized by X-ray diffraction and scanning electron microscopy, respectively. Using above synthesized powders as starting materials, TiAlCo ceramic were successfully prepared by atmospheric plasma spraying (APS) with an internally fed powder torch. Electromagnetic parameters and microwave absorption properties of the prepared ceramic coatings were investigated in the frequency range from 8.2 to 12.4 GHz (X-band). It was found that both the real part and imaginary part of dielectric constant decreases with increasing Al₂O₃ content in the whole measured frequency region. Dielectric properties are closely related to the relaxation polarization and interfacial polarization and electric conductivity. Furthermore, by combination of the frequency selective surfaces (FSS) and prepared coatings, a double absorption band of the reflection loss spectra had been observed in X-band. The optimized reflection loss values exceeding −10 dB can be obtained in the frequency range of X-band when the coating thickness is only 1.8 mm, and the reflection loss is insensitive to incident angle from 0° to 45° for both transverse electromagnetic (TE) and transverse magnetic (TM) polarizations.     

Dielectric and optical properties of electroceramic PBZNZT thin films prepared by pulsed laser deposition process

The 0.6[0.94Pb(Zn_1/3Nb_2/3)O₃ + 0.06BaTiO₃] + 0.4[0.48(PbZrO₃) + 0.52(PbTiO₃)], PBZNZT, thin films were synthesized by pulsed laser deposition (PLD) process. The PBZNZT films possess higher insulating characteristics than the PZT (or PLZT) series materials due to the suppressed formation of defects, therefore, thin-film forms of these materials are expected to exhibit superior ferroelectric properties as compared with the PZT (or PLZT)-series thin films. Moreover, the Ba(Mg_1/3Ta_2/3)O₃ thin film of perovskite structure was used as buffer layer to reduce the substrate temperature necessary for growing the perovskite phase PBZNZT thin films. The PBZNZT thin films of good ferroelectric and dielectric properties (remanent polarization P_r = 26.0 μC/cm², coercive field E_c = 399 kV/cm, dielectric constant K = 737) were achieved by PLD at 400 °C. Such a low substrate temperature technique makes this process compatible with silicon device process. Moreover, thus obtained PBZNZT thin films also possess good optical properties (about 75% transmittance at 800 nm). These results imply that PBZNZT thin films have potential in photonic device applications.     

Structural,electrical, and optical properties of Ti-doped ZnO films fabricated by atomic layer deposition

High-quality Ti-doped ZnO films were grown on Si, thermally grown SiO₂, and quartz substrates by atomic layer deposition (ALD) at 200°C with various Ti doping concentrations. Titanium isopropoxide, diethyl zinc, and deionized water were sources for Ti, Zn, and O, respectively. The Ti doping was then achieved by growing ZnO and TiO₂ alternately. A hampered growth mode of ZnO on TiO₂ layer was confirmed by comparing the thicknesses measured by spectroscopic ellipsometry with the expected. It was also found that the locations of the (100) diffraction peaks shift towards lower diffraction angles as Ti concentration increased. For all samples, optical transmittance over 80% was obtained in the visible region. The sample with ALD cycle ratio of ZnO/TiO₂ being 20 had the lowest resistivity of 8.874 × 10⁻⁴ Ω cm. In addition, carrier concentration of the prepared films underwent an evident increase and then decreased with the increase of Ti doping concentration.     

Electrical and optical properties of plasma polymerized eucalyptus oil films

Electrical and optical properties of the plasma polymerized eucalyptus oil (PPEo) films are discussed in this article. As part of our electrical studies, we have found that the conduction mechanism in the PPEo film is a Schottky type. We have also found that iodine doping can enhance the conductivity of the film. IR studies revealed that PPEo film is a highly crosslinked polymer, and UV‐vis‐NIR studies revealed the information that optical band gap energy of the PPEo film had been reduced as a result of iodine doping. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1102–1107, 2003     

Surface characterization of polyethylene films modified by gaseous plasma

Of the several techniques available for surface modification, plasma processing has proved to be very appropriate. The low temperature plasma is a soft radiation source and it affects the material only over a few hundred angstroms deep, the bulk properties remaining unaffected. Plasma surface treatment also offers the advantage of greater chemical flexibility. The improvement in adhesion was studied by measuring T‐peel strength. In addition, printability of plasma‐treated PE films was studied by cross test method. It was found that printability increases considerably for plasma treatment of short duration. It was therefore thought of as interesting to study the surface composition and morphology by contact angle measurement, ESCA, and AFM. Surface energy and surface roughness can be directly correlated to the improvement in above‐mentioned surface‐related properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 449–457, 2007     

Dielectric,thermal and mechanical properties of hybrid PMMA/RGO/Fe2O3 nanocomposites fabricated by in-situ polymerization

Currently, the organic-inorganic hybrid materials have gained tremendous importance due to their unique applications in different technological fields. In this connection, the chemical synthesis of poly(methyl methacrylate) (PMMA) and its binary and ternary nanocomposites by in-situ bulk polymerization with various percentages of reduced graphene oxide (RGO) and hematite nanoparticles (Fe₂O₃ NPs) is presented. Dielectric properties of binary and ternary nanocomposites are investigated in the frequency range of 25 Hz-1 MHz for each composition. Ternary nanocomposite of PMMA with RGO:Fe₂O₃ NPs (2:2 wt%) exhibits a substantial enhancement of the dielectric constant up to ≈308 and suppressed dielectric loss of 0.12 at 25 Hz. Appearance of three types of interfaces in ternary PMMA nanocomposites accounts for the superior dielectric properties due to the accumulation of greater number of charges at the interfaces as compared to the binary nanocomposites with only one interface. The same optimized ternary PMMA nanocomposite shows a remarkable improvement in the thermal conductivity (2.04 W/mK), which is attributed to the formation of efficient thermal conducting pathways contributed by the synergic reduction in thermal resistance of both RGO and Fe₂O₃ NPs (2:2 wt%) relative to the binary nanocomposites PMMA/2 wt% RGO (1.04 W/mK) and PMMA/2 wt% Fe₂O₃ (0.98 W/mK). Thus, ternary nanocomposites prove to be the excellent candidates for thermal management applications. Furthermore, a comparison of the mechanical strength and thermal stability for all the binary and ternary nanocomposites is presented. In the last section, respective precursors and optimized binary and ternary nanocomposites are characterized by XRD, FTIR and SEM which reveal the strong interaction of respective nanofillers into PMMA matrix.     

Preparation of carboxylate groups-containing thin films by plasma polymerization

Summary Plasma polymerization in a mixture of acrylic acid and carbon dioxide (CO₂) gas was investigated. The polymer deposition rate in plasma polymerization of acrylic acid increased by admixing CO₂ gas, and polymers containing carboxyl groups were formed. The amount of carboxyl groups alterable to carboxylate anions by treating with 0.1 N KOH solution or NH₃ gas reached twice of that formed in plasma polymerization without CO₂ gas.     

Sulfonic acid group-containing thin films prepared by plasma polymerization

Plasam polymerization of hydrocarbon/sulfure dioxide mixtures, C₂H/SO₂, C₂H₄/SO₂, and CH₄/SO₂ mixtures, was investigated to obtain thin films containing sulfonic acid groups. Plasma polymerization of C₂H₂/SO₂ and C₂H₂/SO₂ mixtures gave filmlike products but that of the CH₄/SO₂ mixtures did not. The plasma polymers possessed much amount of sulfur and oxygen moieties with hydrocarbon chains. The sulfur moieties involved thio, sulfite, and sulfonic acid groups. This groups was a main product and reached 70–80 mol % of the total sulfur moieties. The remains (20–30 mol %) were sulfonic acid and sulfite groups. The oxygen moieties were hydroxyl and carbonyl groups with small amount of carbonxyl groups. The plasma polymers showed and hydrophilicity (the surface energy was 54–56mN/m) and good antithrombogenity.     

Structure and properties of oriented polyethylene films

Cast films of a metallocene Linear Low Density Polyethylene (mLLDPE) have been cold‐drawn in the machine direction in two sequential steps to form ultra‐oriented films. The initial films were cast under low shear conditions to form essentially isotropic films, as shown by very low orientation birefringence. The first draw yields moderately oriented films, which display block‐shear type chevron morphology. Under controlled conditions, void formation occurs during the second draw and the ultradrawn films whiten (become opaque), and display a fine crystalline morphology. Surprisingly, the films do not become more permeable; rather, they become high barrier films. In their ultra‐oriented state, the water vapor transmission of the films is equivalent to that of poly(vinylidene chloride) (PVDC). The transport behavior of the films to various gases was studied using transient permeation methods. The decrease in permeability with orientation is attributed to an increase in the degree of crystallinity and increase in tortuosity due to the blocky crystalline morphology. A decrease in the permeability of the amorphous phase due to an increase in the amorphous phase density is also suggested by the data.     

Patterned conductive polyaniline films fabricated using lithography and in situ polymerization

In this article, we describe a novel bottom‐up technique for the preparation of transparent conductive films of polyaniline (PANI). A UV‐curable photoresist was formulated containing an acrylate‐endcapped urethane oligomer [UA(PPG400)], acrylic acid, a photoinitiator, and a reactive diluent (tripropylene glycol diacrylate), and the lithography techniques were used to pattern the structure with line widths/spaces of 100 μm/100 μm, 10 μm/10 μm, and 5 μm/5 μm on a polyethylene terephthalate substrate. The carboxylic acid units on the surface of the patterned photoresist interacted with the aniline monomer units to form anilinium complexes; using ammonium persulfate as a chemical oxidant, we then synthesized a layer of conductive PANI on the surface of the patterned resist through in situ polymerization. The optimal conductivity of the PANI conductive film was ca. 10 S/cm. The thin film was characterized, and its physical properties investigated using Fourier transform infrared spectroscopy, UV–Vis spectroscopy, differential scanning calorimetry, optical and atomic force microscopy, and four‐point probe conductivity measurements. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrical and mechanical properties of polyimide-carbon nanotubes composites fabricated by in situ polymerization

Polyimide (PI)-carbon nanotubes composites were fabricated by in situ polymerization using multi wall carbon nanotubes (MWNT) as fillers. It suggested that in situ polymerization is an ideal technique to make a perfect dispersion of carbon nanotubes into matrixes. Besides it, the pre-treatment of carbon nanotubes in solvent to make the networks untied enough and to let solvent percolated into the networks is very important for forming uniform entanglements between carbon nanotubes and polymer molecular chains. The results imply that the percolation threshold for the electric conductivity of the resultant PI-MWNT composites was ca. 0.15 vol%. The electrical conductivity has been increased by more than 11 orders of magnitude to 10⁻⁴ S/cm at the percolation threshold. The mechanical properties of the polyimide composite were not improved significantly by addition of carbon nanotubes.     

Structural and optical properties of diamond and nano-diamond films grown by microwave plasma chemical vapor deposition

We compare structural and optical properties of microcrystalline and nanocrystalline diamond (MCD and NCD, respectively) films grown on mirror polished Si(100) substrates by microwave plasma chemical vapor deposition. The films were characterized by SEM, Raman spectroscopy, XRD, and AFM. Optical properties were obtained from transmittance and reflectance measurements of the samples in the wavelength range of 200–2000 nm. Raman spectrum of the MCD film exhibits a strong and sharp peak near 1335 cm⁻¹, an unambiguous signature of cubic crystalline diamond with weak non-diamond carbon bands. Along with broad non-diamond carbon bands, Raman spectra of NCD films show features near 1140 cm⁻¹, the intensity of which is significantly higher in the film grown at 600°C compared to the NCD film grown at higher temperature. The Raman feature near 1140 cm⁻¹ is related to the calculated phonon density of states of diamond and has been assigned to nanocrystalline or amorphous phase of diamond. XRD patterns of the MCD film show sharp peaks and NCD films show broad features, corresponding to cubic diamond. The rms surface roughness of the films was observed to be approximately 60 nm for MCD film that reduced substantially to 17 and 34 nm in the NCD films grown at 600 and 700°C, respectively. Tauc's optical gap for the diamond film is found to be approximately 5.5 eV. NCD grown at 700°C has a high optical absorption coefficient in the whole spectral region and the NCD film grown at 600°C shows very high transmittance (∼78%) in the near IR region, which is close to that of diamond. This indicates that the NCD film grown at 600°C has the potential for applications as optical windows since its surface roughness is significantly low as compared to the MCD film.     

Preparation and properties of polyethylene/montmorillonite nanocomposites by in situ polymerization

Polyethylene (PE)/montmorillonite (MMT) nanocomposites were prepared by in situ coordination polymerization using a MMT/MgCl₂/TiCl₄ catalyst activated by Al(Et)₃. The catalyst was prepared by first diffusing MgCl₂ into the swollen MMT layers, followed by loading TiCl₄ on the inner/outer layer surfaces of MMT where MgCl₂ was already deposited. The intercalation of MMT layers by MgCl₂ and TiCl₄ was demonstrated by the enlarged interlayer spacing determined by WAXD. The nanoscale dispersion of MMT layers in the polyethylene matrix was characterized by WAXD and TEM. As a consequence, the crystallinity of the nanocomposite decreased sharply, whereas the tensile strength was significantly improved compared to that of virgin polyethylene of comparable molecular weight. The confinement of the nanodispersed MMT layers to molecular chain and the strong interaction between the nanoscale MMT layers and the resin matrix were thought to account for the decrease of crystallinity and the remarkable enhancement of strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3680–3684, 2003     

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.     

Dielectric properties of alumino-silicate ceramics synthesized by plasma sintering

The polycrystalline ceramic specimens of three different alumino-silicate solid solutions (Al_0.70Si_0.30O, Al_0.73Si_0.27O and Al_0.75Si_0.25O) consisting of different alumina and silica concentrations have been synthesized by thermal plasma sintering technique. From structural analysis carried out by X-ray diffraction, the ceramics are mostly found to consist of two different phases of mullite and sillimanite. SEM images of these ceramics reveal a high dense and less porous microstructure with homogeneous distribution of grains throughout their surface. These materials exhibit high dielectric constant value (>10³) with low dissipation factor. The AC conductivity analysis reveals that Al_0.70Si_0.30O and Al_0.75Si_0.25O ceramics possess room temperature conductivity values of the order of 10^?5, whereas Al_0.73Si_0.27O has conductivity of 10^?7 order that increases with rise in temperature. From the Nyquist plots, the grain and grain boundary conductivities are distinguished and negative temperature coefficient of resistance behavior is identified in these ceramics with small positive temperature coefficient of resistance effect.     

Modification of polyethylene surface using plasma polymerization of silane

In the present study plasma polymerization of tetraethylorthosilicate and hexamethyldisiloxane was carried out on polyethylene film with an aim of enhancing barrier properties. The glow discharge was obtained at 0.2 mbar using 13.56 MHz radio frequency source capable of giving power out put up to 100 W. The monomer vapors were passed in the system at the rate of 15 SCCM. The extent of deposition was determined from the weight gain study and the morphology was studied using SEM. Films were further characterized by surface energy measurement, ATR‐FTIR and ESCA analysis. Since PE is widely used for packaging and in this process a thin layer of glass‐like transparent SiOx was deposited, therefore it was thought necessary to study permeability to water vapors. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Dielectric and conduction properties of pure polyimide films

Capacitors with an Al–polyimide–Al sandwich film structure have been fabricated: the top and the bottom aluminium electrodes were deposited by vacuum evaporation and the polyimide film was deposited by an isothermal immersion method. An X‐ray diffractogram of the film indicates the amorphous nature of the polyimide film. Dielectric and ac conduction properties of polyimide capacitors in the frequency range 10 kHz to 10 MHz at various temperatures (303–423 K) are reported; the dc conduction at different voltages and at various temperatures (303–423 K) is given. The capacitance of the film decreases with increasing frequency but increases with increasing temperature. The ac conduction studies suggest that electron hopping is responsible for conduction while the dc conduction studies reveal that Poole–Frenkel conduction is predominant at high fields. The activation and zero field activation energies are also calculated. © 2001 Society of Chemical Industry     

An optical microstructural model for blown polyethylene films

This paper presents an optical microstructural model showing, the behavior of blown low‐density polyethylene films as optical polymers (birefringence and anisotropy), at a structural level. The model is mainly based on a microstructural study involving the observation and analysis of increasingly smaller structures by transmission electron microscopy, POM, and X‐ray diffraction, as a means of calculating the values of their orientation functions (the uniaxial approximation). These values enabled us to indicate graphically the most probable average position of the unit cell (the natural scale of our model) and hence of other crystalline structures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1708–1720, 2000     

Dynamic mechanical properties of methacrylic-acid-grafted polyethylene films

A dynamical mechanical relaxation study has been made of low density polyethylene films to which methacrylic acid has been grafted by γ irradiation. The grafted films retain the original degree of crystallinity and show only slight changes in melting points and melt viscosities. This indicates that the grafted methacrylic acid side chains are long, few in number, and completely phase separated from the polyethylene matrix. Three dispersion regions are observed in plots of the loss modulus, E″ vs. temperature at constant frequency and these are labeled γ, β, α′, in order of increasing temperature. The α′ peak, above 215°C was assigned to microbrownian segmental motions accompanying the T_g of polymethacrylic acid. The β peak, at ?20°C, was assigned to motions accompanying the T_g of branched polyethylene, and the γ peak, at ?120°C, was assigned to local motions of a few CH₂ sequences in polyethylene.     

Structure and properties of films fabricated from chitin solution by coagulating with heating

In the present work, chitin films were fabricated from chitin solution dissolved in 8 wt % NaOH/4 wt % urea aqueous systems at low temperature by coagulating with heating without using any coagulant. The formation of the chitin films was confirmed to be an entirely physical process, namely chitin inclusion complex associated with NaOH, urea and water in the solvent was broken by heating, leading to the aggregation of the chitin chains through the hydrogen bonding. A schematic model was proposed to describe the regeneration mechanism of the chitin, indicating the physical crosslinking and entanglement of the chitin chains to form the films. Glycerol was used as plasticizer, and with an increase of the glycerol content, the elongation at break (?_b) of chitin films increased rapidly from 7.8 to 83.1%, whereas the tensile strength (σ_b) decreased from 89.3 to 51.7 MPa. This work provided a “green” pathway for the researches and developments of chitin materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39538.