Syntheses and characterisation of electrically conductive and fluorescent poly[3-(ω-bromoalkyl)thiophenes]

A novel series of functionalized polythiophenes incorporating 3-(ω-bromoalkyl) pendants were synthesized by chemical oxidative polymerization using FeCl₃ and characterized using FT-IR, UV–Vis absorption spectroscopy, fluorescence emission spectroscopy, conductivity measurements and thermal analyses. These polymers attained a maximum electrical conductivity between 4.7 and 8.4 S cm⁻¹ upon doping with iodine and have a fluorescence quantum yield of up to 11.1% with respect to quinine sulfate. The influence of the terminal ω-bromine substituent as of the length of the alkyl pendant on electrical conductivity, spectral behavior and thermal stability is discussed.     

Electrically conducting poly[3-(ω-hydroxyalkyl)thiophenes]

A series of poly[3-(ω-hydroxyalkyl)thiophenes] was synthesized by chemical oxidative polymerization using FeCl₃ and characterized by FT-IR, thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Upon doping with iodine the polymers attained electrical conductivities of between 0.5 and 38 S cm⁻¹. Electrical conductivities of doped samples were found to increase with alkyl chain lengths, being optimum for the octyl pendant moiety. Thereafter, the conductivity decreased, as the doping and dedoping for the polymers became more difficult. Increasing the hydrocarbon chain length of the pendant substituent also resulted in decreased thermal stability of the polymers. XPS results showed that some C–OH groups in the polymers were oxidized to CO in the polymerization process.     

Synthesis and characterization of new light-emitting copolymers containing 3,4-dialkoxythiophenes

We report the synthesis, optical and electrochemical properties of a new series of polyoxadiazoles (P1–P3) consisting of 3,4-dialkoxythiophene and 1,4-divinylbenzene units. The polymers are prepared using the precursor polyhydrazide route. The polymers have well defined structure and exhibit good thermal stability with the onset decomposition temperature in nitrogen at around 330 °C. The optical and charge-transporting properties of the polymers are investigated by UV–vis spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. The UV–vis absorption spectra of polymers in solution showed a maximum at around 380 nm. The polymers depicted bluish-green fluorescence in solutions and green fluorescence in thin films. Cyclic voltammetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from 3.25 to 3.31 eV and HOMO energy levels ranging from 5.48 to 5.56 eV, which indicated that the polymers are expected to provide enhanced charge-transporting (electron transport/hole blocking) properties for the development of efficient polymer light-emitting diodes (PLEDs).     

Low thermal conductivity without oxygen vacancies in equimolar YO1.5 + TaO2.5- and YbO1.5 + TaO2.5-stabilized tetragonal zirconia ceramics

A narrow range of composition exists along both the ZrO₂–YTaO₄ and ZrO₂–YbTaO₄ quasi-binaries over which the tetragonal zirconia phase can be retained on cooling. Unlike other stabilized zirconia materials which have low thermal conductivity as a result of phonon scattering by oxygen vacancies, these compositions do not contain oxygen vacancies and yet an equimolar YO_1.5 + TaO_2.5 composition has been reported to also exhibit low thermal conductivity [1]. We find that zirconia compositions along the quasi-binaries have low and temperature-independent thermal conductivities, and that the thermal conductivities and their temperature dependence are consistent with a defect scattering model that takes into account a minimum phonon mean free path due to the inter-atomic spacing. Furthermore, the conductivities of the Yb and Y trivalent-doped compositions scale in a predictable manner with atomic site disorder effects on the cation sub-lattice associated with the lighter Y³⁺ ions and the heavier Yb³⁺ and Ta⁵⁺ ions. The lowest thermal conductivity measured was ～1.4 W mK^–1 at 900 °C. The low thermal conductivity and phase stability makes these systems promising candidates for low conductivity applications, such as thermal barrier coatings.     

The effect of low-temperature conditions on the electrochemical polymerization of polypyrrole films with high density,high electrical conductivity and high stability

High-quality polypyrrole-hexafluorophosphate (PPy-PF₆) films with high density (∼1.4 g/cm³), high conductivity (>300 S/cm for unstretched film) and high electrochemical stability are obtained reproducibly by galvanostatic polymerization at low-temperature conditions. The optimal polymerization current density of J_p=0.02–0.05 mA/cm² was obtained at the polymerization temperature of T_p=−40°C. The surface morphology of the film sensitively varies depending upon the properties of electrode and its surface conditions. The transport measurements characterize the high-density PPy-PF₆ film as a disordered metal close to the boundary of disorder induced metal–insulator (M–I) transition. The X-ray diffraction measurements suggest that partially crystalline structure of PPy-PF₆ film is related to the transport properties. The uniaxial stretching induces an increase of the conductivity up to ∼930 S/cm in a direction parallel to stretching as well as the anisotropy of conductivity. The comparative studies of thermogravimetric analysis (TGA), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for PPy-PF₆ films prepared at room-temperature and low-temperature conditions show that the latter exhibit better thermal stability as well as electrochemical stability under long oxidative polarization.     

Effects of dopants and polymer structures on electrical conductivity of organosilicon polymers

A series of organosilicon polymers comprising disilanylene-phenylene, disilanylene-ethynylene and disilanylene-(bisethynylene-phenylene) chains carrying dibutyl or phenyl and methyl groups as side chains, and polysilanes carrying alkyl, aromatic or heteroaromatic side chains were synthesized. The electrical conductivities of their polymers doped with electron acceptors such as I₂, FeCl₃ and SbF₅ were measured by using vapor-phase doping. The electrical conductivities of organosilicon polymers doped with I₂ showed a good correlation with the ionization potentials of the original polymers. In contrast, in the case of SbF₅ doping, the degradation of polymers occurred and every polymer gave the same order of conductivity, 10⁻⁴−10⁻³ S/cm. The polymers carrying heteroaromatic substituents gave the higher conductivity by doping with I₂, while in the case of the polymers carrying phenyl groups, the conductivity was enhanced by doping with FeCl₃.     

Polypyrrole as a solid electrolyte for tantalum capacitors

Tantalum/tantalum pentoxide (Ta/Ta₂O₅)-based capacitors, in which polypyrrole (PP) is used as a solid electrolyte coating, have been studied. Aromatic sulfonate salts were used as the charge-compensating dopant ions due to their ability to impart good thermal and long-term stability. The capacitors prepared showed excellent high frequency performance up to 100 kHz and stability. The capacitors were prepared by two methods. In the first method the Ta₂O₅ dielectric layer was coated with chemically synthesized PP, followed by electrodeposition of a second layer of PP to increase the thickness and integrity of the PP layer. In the second method, chemical polymerization was used alone and the process repeated several times in order to obtain complete coverage of the Ta/Ta₂O₅, anodes. The redox properties of the PP synthesized chemically and electrochemically were studied by cyclic voltammetry and indicate that the polymers have similar electrochemical properties. Compositional analyses were carried out using X-ray photoelectron spectroscopy (XPS) before and after the re-anodization process used in the capacitor preparation to enhance the integrity of the TaTa₂O₅ dielectric. UV-Vis spectroscopy was used to check the stability of the PP to spontaneous ion exchange during the re-anodization process. The results indicate that aromatic sulfonates remain as the dopant ions when the reformation is carried out in the same aromatic sulfonate solution, but are partially substituted by H₂PO₄^- when the reformation is carried out in H₃PO₄. For the chemical polymerization, different synthetic conditions were used in order to improve the conductivity of PP; specifically, the use of low temperature and the addition of p-nitrophenol reduce the equivalent series resistance (ESR) of the capacitors.     

Thermal conductivity of titanium dioxide films grown by metal-organic chemical vapor deposition

We studied the effect of the microstructures on the thermal conductivity of the titanium dioxide (TiO₂) films. TiO₂ films were grown by MOCVD, their morphologies were observed using a scanning electron microscope (SEM). The chemical composition was determined through Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) measurements. The thermal conductivity of the in-plane direction was measured using an alternating current calorimetric method (laser-heating Angstrom method) in the temperature range of 300 to 470 K. The authors fabricated a TiO₂ film with extremely low thermal conductivity (~ 0.5 Wm^− 1 K^− 1), in which a feather-like texture is regularly arranged in the direction perpendicular to the heat flow. The origins of the extremely low thermal conductivity were studied from a microstructural viewpoint.     

Syntheses and investigation of polymers containing 1-triazene-1,3-diyl and 1,4-phenylene group

Triazene-group-containing polymers have been synthesized from p-phenylenediamine precursors by diazotization and azo-coupling methods. For this purpose, two pathways have been used. The effect of monomer/sodium nitrite ratio on the solubility of the polymers, as well as the dependence of properties such as electrical conductivity and ESR upon the main chain structure, have been investigated. Solubility tests showed that the lower the sodium nitrite/p-phenylenediamine molar ratio (<1), the higher the solubility of the resulting polytriazene. ¹H NMR, IR, and UV/vis absorption spectroscopies have been used to elucidate the chemical structures of the polymers obtained. Electrical conductivity studies and ESR measurements have been conducted on both as-synthesized and doped polymer samples. The room temperature electrical conductivity of the obtained polymers was found to increase from 10^?11–10^?9 to 7 × 10^?3–2 × 10^?2 S/m upon doping with iodine. According to ESR spectroscopy data, this increase in conductivity may be attributed to improved charge carrier (polaron) mobility. An important feature of these polymers is that their conductivity may be increased up to 10^?4 S/m by doping with hydrochloric and sulfuric acids.     

Synthesis and characterization of oxazinone and oxazoline substituted pyrroles: Towards electrically conducting bi-functional copolymers

The synthesis of N-(3-aminopropyl)pyrrole and N-(2-carboxyethyl)pyrrole was reviewed and repeated. Both compounds were utilized as pre-cursors for the synthesis of oxazinone and oxazoline modified pyrroles by different synthetic pathways. The N-substituted pyrroles were characterized by ¹H NMR, ATR-FTIR, and MALDI-TOF MS. The chemical oxidative copolymerization of pyrrole and its derivatives was carried out in various solvent systems using FeCl₃ and (NH₄)₂S₂O₈ as oxidants. Furthermore, sodium poly(styrene sulfonate) was used as dopant leading to core-shell-like structures, and, after the copolymerization of pyrrole with oxazinone or oxazoline functionalized monomers, to exceptionally increased conductivities. The produced (co-)polymers were characterized in terms of their chemical composition, morphology, and electrical conductivity. Oxazinone and oxazoline moieties in the copolymers were confirmed by ATR-FTIR. Furthermore, the retained reactivity of oxazinone and oxazoline functions after chemical oxidative copolymerization was evidenced by model reactions with 1-pyrenemethylamine and 1-pyreneacetic acid, respectively, and subsequent fluorescence microscopy and spectroscopy.     

Poly(2,5-dialkoxy-p-phenylenebutadiynylene)s—Novel rigid conjugated polymers with liquid crystalline property

Novel rigid conjugated poly(p-phenylenebutadiynylene)s having long alkoxy side chains, octyloxy (C8), decyloxy (C10), and dodecyloxy (C12) at 2,5-positions of a phenylene unit, are synthesized by oxidative polycondensation of corresponding 2,5-dialkoxy-1,4-diethynylbenzenes with Hay catalyst. The polymers are soluble in hot solvents such as CHCl₃ and fusible upon heating. UV–Vis spectra of the polymers show an absorption maximum (λ_max) around 420 nm due to the π-conjugation along the main chain. An intense fluorescence exhibiting the λ_max around 475 nm is observed in all of the polymers. Cyclic voltammetry of the polymer shows two Li ion-participated redox reactions occurred at the dialkoxyphenylene moiety and in the conjugated polymer chain due to an n-doping process. Electrical conductivity is an order of 10⁻⁸ S cm⁻¹ which increases to an order of 10⁻⁴ S cm⁻¹ upon vapor phase doping by H₂SO₄. Thermochemical investigations by DSC and polarized optical microscopy suggest that the polymers have a nematic liquid crystalline phase. The molecular arrangements in the phase is evaluated by XRD and a molecular dynamics simulation. A nematic phase is shown to arise from a side-by-side accretion of the rigid rodlike main chains. A lamellar structure is suggested in the crystalline phase.     

Effect of lattice defects on thermal conductivity of Ti-doped,Y2O3-stabilized ZrO2

The evolution of lattice structure and thermal conductivity has been studied systematically for a range of Ti-doped, Y₂O₃-stabilized ZrO₂ (YSZ) solid solutions. The mechanism of reducing the thermal conductivity by Ti doping has been determined. Ti⁴⁺ mainly substitutes for Zr⁴⁺ below a critical composition factor (x ? 0.08), above which the interstitial Ti⁴⁺ need to be considered separately. The effect of lattice defects caused by mass and radius differences between Ti⁴⁺ and Zr⁴⁺ ions on the phonon scattering coefficient was discussed quantitatively. And the reduction of oxygen vacancy by interstitial Ti⁴⁺ ions which increases the thermal conductivity at high Ti doping content was also determined. Concerning the integrated phase stability and thermo-mechanical properties, Ti-doped YSZ is believed to be a promising candidate for thermal barrier coatings at higher temperature.     

Synthesis,characterization and properties of highly conducting organometallic polymers derived from the ethylene tetrathiolate anion

The preparation and electrical conductivity studies of a series of organometallic polymers, (MC₂S₄^x−)_n (M = Ni, Pd, Pt, Au), derived from the ethylene tetrathiolate anion are described. The synthesis of the precursor molecules or molecular complexes (PhCH₂)₄(C₂S₄), (AsPh₄)₂[M(C₃OS₄)₂], (C₃)OS₄Pd(dppe) and (AsPh₄)₂[(C₃OS₄)Cu(C₂S₄)Cu(C₃OS₄)] is also described. From these results the different possible formation mechanisms of the polymers are discussed. The polymers show high compaction powder conductivity at room temperature (from 10⁻⁵ to 5Ω⁻¹ cm⁻¹). [Na_0.31(NiC₂S₄)]_ν, one of the most conductive polymers, exhibits a metal-like temperature dependence of conductivity, as evidenced by voltage shorted compaction (VSC) experiments. These conductivity properties are to be related with the degree of partial oxidation (DPO) observed in the polymers studied.     

Microstructure and Thermomechanical Properties of Atmospheric Plasma-Sprayed Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating

In this study, a Yb₂O₃ coating was fabricated by the atmospheric plasma spray technique. The phase composition, microstructure, and thermal stability of the coating were examined. The thermal conductivity and thermal expansion behavior were also investigated. Some of the mechanical properties (elastic modulus, hardness, fracture toughness, and flexural strength) were characterized. The results reveal that the Yb₂O₃ coating is predominantly composed of the cubic Yb₂O₃ phase, and it has a dense lamellar microstructure containing defects. No mass change and exothermic phenomena are observed in the thermogravimetry and differential thermal analysis curves. The high-temperature x-ray diffraction results indicate that no phase transformation occurs from room temperature to 1500 °C, revealing the good phase stability of the Yb₂O₃ coating. The coefficient of thermal expansion of the Yb₂O₃ coating is (7.50-8.67)?×?10^?6 K^?1 in the range of 200-1400 °C. The thermal conductivity is about 1.5 W m^?1 K^?1 at 1200 °C. The Yb₂O₃ coating has excellent mechanical properties and good damage tolerant. The unique combination of these properties implies that the Yb₂O₃ coating might be a promising candidate for T/EBCs applications.     

Improved Thermal Performance of Diamond-Copper Composites with Boron Carbide Coating

B₄C-coated diamond (diamond@B₄C) particles are used to improve the interfacial bonding and thermal properties of diamond/Cu composites. Scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were applied to characterize the formed B₄C coating on diamond particles. It is found that the B₄C coating strongly improves the interfacial bonding between the Cu matrix and diamond particles. The resulting diamond@B₄C/Cu composites show high thermal conductivity of 665 W/mK and low coefficient of thermal expansion of 7.5 × 10^?6/K at 60% diamond volume fraction, which are significantly superior to those of the composites with uncoated diamond particles. The experimental thermal conductivity is also theoretically analyzed to account for the thermal resistance at the diamond@B₄C-Cu interface boundary.     

Conductivity, Mechanical and Thermal Studies on Poly(methyl methacrylate)-Based Polymer Electrolytes Complexed with Lithium Tetraborate and Propylene Carbonate

A series of different composition ratio of polymer electrolytes based on poly(methyl methacrylate) (PMMA) as host polymer, lithium tetraborate (Li₂B₄O₇) as salt, and propylene carbonate (PC) as plasticizer is produced by solution casting method. Fourier transform infrared (FTIR) spectroscopy studies are used to confirm the formation of polymer electrolyte complex. PMMA: Li₂B₄O₇: PC (52.5:22.5:25.0 wt.%) is obtained as the highest conducting polymer electrolyte with a conductivity of 5.14 × 10⁻⁶ S/cm at room temperature (23 °C). The temperature-dependent conductivity of the polymer films shows Arrhenius-like behavior which reveals that the charge carriers move in a liquid-like environment. The addition of PC decreases the Young’s modulus and stress at peak values of the complexes. Thermogravimetric analysis (TGA) is employed to study the thermal stability of the electrolytes.     

Preparation and characterization of a polypyrrole hybrid film with [Ni(dmit)2]2−, bis(1,3-dithiole-2-thione-4,5-dithiolate)nickellate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Ni(dmit)₂] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in acetonitrile solution is reported. The material was characterized by cyclic voltammetry, UV–vis and infrared spectroscopies, scanning electron microscopy (SEM), atomic force microscopy (AFM) and thermal gravimetric analysis (TGA). The FTIR spectroscopy showed that the [Ni(dmit)₂]²⁻ anion has been inserted in the polypyrrole framework and was not destroyed or modified during the polymerization process. The voltammetric analysis indicated that the material has electroactivity and undergoes redox processes associated with the conducting polymer and the counteranion. The cyclic voltammetry results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Ni(dmit)₂]²⁻ exhibits good thermal stability and a intrinsic conductivity value in the range of semiconductors (10⁻³ S cm⁻¹).     

Comparison of Single-Phase and Two-Phase Composite Thermal Barrier Coatings with Equal Total Rare-Earth Content

Rare-earth zirconates have been the focus of advanced thermal barrier coating research for nearly two decades; however, their lack of toughness prevents a wide-scale adoption due to lack of erosion and thermal cyclic durability. There are generally two methods of improving toughness: intrinsic modification of the coating chemistry and extrinsic modification of the coating structure. This study compares the efficacy of these two methods for a similar overall rare-earth content via the air plasma spray process. The extrinsically toughened coatings were comprised of a two-phase composite containing 30 wt.% Gd₂Zr₂O₇ (GZO) combined with 70 wt.% of a tougher t′ low-k material (ZrO₂-2Y₂O₃-1Gd₂O₃-1Yb₂O₃; mol.%), while a single-phase fluorite with the overall rare-earth content equivalent to the two-phase composite (13 mol.% rare-earth) was utilized to explore intrinsically toughened concept. The coatings were then characterized via x-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy, and their performance was evaluated via erosion, thermal conductivity, thermal annealing (500 h), and thermal cycling. It was shown that the extrinsic method provided an improved erosion and thermal conductivity response over the single phase, but at the expense of high-temperature stability and cyclic life.     

Microstructure and Properties of Porous Ni50Cr50-Al2O3 Cermet Support for Solid Oxide Fuel Cells

The microstructure of the cermet support significantly influences the performance of solid oxide fuel cells (SOFCs). The properties required for the support include high electrical conductivity, necessary permeability, good match of thermal expansion with other layers, and high strength. In this study, a flame-sprayed porous Ni50Cr50-Al₂O₃ cermet was designed as the support of SOFCs. The effect of cermet microstructure on its gas permeability, electrical conductivity, thermal expansion coefficient (TEC), and bending strength was investigated. Results show that the gas leakage rate of the cermet increased with the increase of polyester content in the starting powder. The cermet exhibited a thermal expansion coefficient of 11.39 × 10^?6 K^?1 from 25 to 1000 °C. Moreover, the electrical conductivity of the cermet increased significantly and reached 1015 S/cm after sintering at 1000 °C for 15 h. The bending strength of the cermet reached 171 MPa. The cermet stability at high temperatures and SOFCs’ performance are discussed.     

Microstructure and Thermophysical Properties of SrZrO<Subscript>3</Subscript> Thermal Barrier Coating Prepared by Solution Precursor Plasma Spray

Strontium zirconate (SrZrO₃) thermal barrier coatings were deposited by solution precursor plasma spray (SPPS) using an aqueous precursor solution. The phase transition of the SrZrO₃ coating and the influence of the aging time at 1400 °C on the microstructure, phase stability, thermal expansion coefficient, and thermal conductivity of the coating were investigated. The unique features of SPPS coatings, such as interpass boundary (IPB) structures, nano- and micrometer porosity, and through-thickness vertical cracks, were clearly observed evidently in the coatings. The vertical cracks of the coatings remained substantially unchanged while the IPB structures gradually diminished with prolonged heat treatment time. t-ZrO₂ developed in the coatings transformed completely to m-ZrO₂ phase after heat treatment for 100 h. Meanwhile, the SrZrO₃ phase in the coatings exhibited good phase stability upon heat treatment. Three phase transitions in the SrZrO₃ coatings were revealed by thermal expansion measurements. The thermal conductivity of the as-sprayed SrZrO₃ coating was ~1.25 W m^?1 K^?1 at 1000 °C and remained stable after heat treatment at 1400 °C for 360 h, revealing good sintering resistance.