Polarization properties of the Raman spectra in neutral and iodine doped cis-trans (CH)x

Polarized resonant Raman spectra of oriented cis-trans -(CH)_x are presented for undoped and iodine doped samples. For undoped films the depolarization ratios of cis lines are consistent with a fibrils misorientation of about 20°. Similar values of depolarization ratios have been measured in iodine doped films as well as for the cis and trans lines than for I₃⁻ mode. These results mean that doping does not destroy the orientational ordering of polymer chains and that under doping the iodine takes the orientation of these chains.     

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.     

Spectroscopic and conductivity studies of doping in chemically synthesized poly(3,4-ethylenedioxythiophene)

Spectroscopic methods (Raman (514.5 nm excitation), infrared (IR), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR)) and electrical conductivity measurements were used to characterize the electrically conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) prepared by persulfate oxidation under aqueous conditions. Elemental analysis was carried out on the resulting sulfate-doped PEDOT to determine the sulfate doping level. Due to the difficulty in dedoping highly stable p-doped PEDOT, the sulfate-pre-doped PEDOT was directly treated with iodine solution in order to investigate the secondary doping processes between PEDOT and iodine. Two processes were observed: (1) the further oxidation of the polymer by iodine to produce an increase in the doping level, with triiodide as the dopant and (2) the replacement of sulfate by triiodide in an ion-exchange process involving triiodide in equilibrium with iodine in the iodine solution. Conductivity studies, in conjunction with XPS and EPR experiments, were used to analyse the relationship between the doping level and conductivity that was explained by differences in the nature of SO₄²⁻ and I₃⁻ as dopant ions and a shift in the polaron/bipolaron equilibrium. The Raman spectra (785 nm excitation) of these PEDOT samples were also investigated and a significant change has been observed in the wavenumber of the symmetric C_α = C_β stretching bands with varying levels of dopants. A correlation was observed between the ratio of the integrated intensities of the symmetric C_α = C_β stretching bands and the doping level in PEDOT that can be useful for estimating the doping level of a PEDOT sample from its Raman spectrum.     

An in situ ESR study on poly(3-methylthiophene): charge transport due to polarons and bipolarons before the evolution of metallic conduction

In situ ESR measurements with ClO₄⁻-doped poly(3-methylthiophene) (PMT) are carefully performed over a wide range of doping level from 0.02% to 23% in order to correlate a drastic increase of carrier mobilities by doping with the nature of charged species in the π-conjugated polymer. Either or both of a Gaussian and Lorentzian components with different g-factors are observed, depending on the doping level. The broad Gaussian signal ascribable to structural defects in the polymer remains almost unchanged at various doping stages while the Lorentzian signal varies greatly with the doping level. From spin concentrations for the Lorentzian signal, molar fractions of polarons and diamagnetic species (bipolarons) are evaluated as a function of doping level. Combination of the molar fractions and the mobility data obtained earlier demonstrates that the conduction process in the lightly doped PMT film (0.02%–1%) can be expressed by independent driftings of polarons and bipolarons under electric field, whose mobilities are 2×10⁻⁵ and 10⁻³ cm² V⁻¹ s⁻¹, respectively. At higher doping levels of 1%–23%, conductivity is much more enhanced than expected from this model and the line width of the Lorentzian signal increases from 1.2 to 7.5 G, suggesting the evolution of a metallic conduction.     

Electric properties of iodine-doped polyacetylene

Results of d.c. and microwave conductivities and dielectric constant measurements on iodine-doped (CH)_x are reported. The gradual variation of the transport properties as a function of the iodine concentration indicates that no sharp phase transition occurs with increasing doping levels. Charged π-phase kinks localized around I₃^? qualitatively describe the dielectric properties in the lightly doped range.     

Evidence for different equilibrium regimes in poly (phenylacetylene)-iodine solutions by means of low-frequency electrical conductivity measurements

The electrical conductivity of poly (phenylacetylene)-iodine in tetrahydrofuran solutions has been measured at the frequency of 10 kHz, at different polymer concentrations in the presence of different amounts of iodine up to a concentration of 20 mg ml⁻¹. The data have been analysed in the light of current theories of polyelectrolyte solutions, considering the effect of counterions along the charged polymer chain. The dependence of the electrical conductivity on the iodine concentration suggests that the conduction mechanism is governed by different equilibria, resulting in two different charge-transfer complexes, PPA⁺I₅^{poststaggered−} and PPA⁺I₃^{poststaggered−}; both of them can give rise to ion fluctuation.     

Poly(3′,4′-dibutyl-α-terthiophene-phenylene-vinylene): a new soluble and dopable phenylene-vinylene-based conjugated polymer

A new soluble and dopable copolymer consisting of 3′,4′-dibutyl-2,2′:5′,2″-terthiophene and phenylene-vinylene units has been designed and prepared via a Wittig reaction. This title copolymer is soluble in common organic solvents such as THF and CHCl₃, and can be doped with iodine achieving an electrical conductivity of about 3.2 × 10⁻² S/cm at room temperature. Films of this copolymer are electroactive and turn reversibly and rapidly from red to green-blue upon doping and undoping electrochemically.     

Swelling of polyacetylene when doped by iodine or sodium

Measurement of swelling of cis polyacetylene during doping with iodine or sodium, and the relative compensations, have been carried out by an original technique. The use of a tensile micromachine has allowed in situ conductivity and precise length measurements. A linear dependence of volume with iodine concentration per carbon atom y_I, is observed over a wide range of concentration (5% >y_I > 13%). A 1% y_I increase causes a 3% volume expansion. This value is very close to the one deduced from the structural model of Baughman et al. Similar results are obtained with sodium doping.During doping, compensation, and redoping, a continuous volume increase is observed, up to a 40% augmentation. Thus the volume effects of the dopants in the sample are cumulative.     

E.S.R. of BF4−-doped polythiophene

We have studied poly(3-methylthiophene) doped electrochemically with BF₄⁻ by electron spin resonance. The spin concentration increases linearly by about one spin per injected charge up to quite high doping levels (≈ 10 mol% at room temperature). The magnetic susceptibility χ_m(T) gradually changes from a Curie- to a Pauli-type behaviour with increasing doping concentration. Simultaneously, an increasing degree of delocalization of the corresponding spin centres is inferred from linewidths, line shape analysis and spin-lattice relaxation rates. The metallic behaviour observed by e.s.r. at high doping levels is attributed to a microscopic electrical conductivity, which is higher than the macroscopic one observed by transport measurements by a factor of about 50. The present results demonstrate that polarons are the dominant charge states in poly(3-methylthiophene) doped with BF₄⁻.     

Low-frequency electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solutions: effect of iodine concentration

The electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solution has been measured at the frequency of 10 kHz, in the temperature range from −15 to 40 °C as a function of iodine concentration. The data have been analysed on the basis of the counterion fluctuation model developed for highly charged polyelectrolyte aqueous solutions. The dependence of the electrical conductivity on the iodine concentration suggests that the conduction mechanism is governed by the interaction of the polymer with iodine molecules, resulting in a charge-transfer complex in solution, the effectiveness of which is maximum at some well-defined concentrations corresponding to six polymer units for each I₅⁻ ion.     

Polyaniline with ω-hydroxyalkoxy pendant substituent on the meta-position

A series of meta-substituted polyaniline derivatives, poly[3-(ω-hydroxyhexoxy)aniline], poly[3-(ω-hydroxyoctoxy)aniline], poly[3-(ω-hydroxydecoxy)aniline] and poly[3-(ω-hydroxydodecoxy)aniline] have been synthesized via chemical oxidative polymerization. The resulting polymers show enhanced solubility in organic solvent. The polymerization yield is increased and the reaction is accelerated by the addition of aniline. The homopolymers can attain conductivity in the range of 10⁻⁶ to 10⁻⁴ S cm⁻¹ after protonic doping with HCl. Upon doping oxidatively with iodine, the conductivity is ca. 10⁻⁵ to 10⁻³ S cm⁻¹. For the copolymers with aniline (15 mol%), the corresponding conductivity is higher, 10⁻⁵ to 10⁻³ S cm⁻¹ upon HCl doping and 10⁻⁴ to 10⁻² S cm⁻¹ upon iodine doping. Thermogravimetry (TG) of the polymer depicts two major weight loss steps corresponding to the degradation of side chain and the thermal breakdown of the backbone, respectively. The polymers are largely amorphous but show an increase in crystallinity with increasing pendant chain length. The polymers were also subjected to FT-IR, UV–VIS and X-ray photoelectron spectroscopy (XPS) studies.     

Novel `synthetic metals' based on symmetrically tetrasubstituted nickel phthalocyanines

Nickel(II) 2,9,16,23-tetrasubstituted phthalocyanines, NiPTX (where X=–OH, –NO₂, –NH₂ and –SO₃H) were synthesized in pure state and doped with iodine. Elemental analysis, UV-Vis, infrared, X-ray diffraction, magnetic susceptibility and TGA studies were used to investigate the effects of iodine doping as well as substituents on the properties of the complexes. The electrical conductivity of nickel phthalocyanine derivatives found to depend on the nature of the substituents and showed ∼10³–10⁵ times increased electrical conductivity in comparison to parent nickel phthalocyanine. Further, the substitution and iodine doping show remarkably very high improved electrical conductivity nearly 10¹¹ times the electrical conductivity of nickel phthalocyanine.     

Tetra(9,10-phenanthro)tetraazaporphyrin - phthalocyanine: Comparative electrical conductivities

Tetra(9,10-phenanthro)tetraazaporphyrin, H₂TPTAP, has been synthesized and characterized for comparative electrical conductivity measurements with phthalocyanine, H₂Pc, before and after iodine doping. The objective is to determine the effect on conductivity of fusing eight additional benzo rings to the periphery of the phthalocyanine ring. H₂Pc doped to a (H₂Pc)I_2.5 composition with a resistivity decreases from 10¹⁵ to 1 ω cm, while H₂TPTAP doped to a (H₂TPTAP)I_0.26 composition with a corresponding resistivity change from 10¹¹ to 10⁸ ω cm. Experimental data and the literature indicate that benzene rings fused to the periphery of the tetraazaporphyrin ring have little π-electron interaction. Similarly, the structure-conductivity correlation of data is interpreted as indicating that fusion of additional benzo rings has an insulating substituent group effect on oxidation of and charge transport between the tetraazaporphyrin rings in the polycrystalline solid.     

Chemical polymerization of aniline using periodic acid in acetonitrile

The chemical polymerization of aniline in anhydrous medium was investigated using periodic acid, H₅IO₆ as an oxidant. This is the first time that H₅IO₆ has been used as an oxidant in the chemical synthesis of conductive polymers. The product was characterized by FTIR, UV–vis spectroscopies, scanning electron microscope (SEM), energy dispersive X-ray (EDX) spectroscopy, thermogravimetric (TG) analysis, and electrical conductivity measurements. EDX and thermogravimetric analysis showed that Pani includes ClO₄⁻ and iodine or iodide ion as dopants. Electrical conductivity of polyaniline with H₅IO₆ was measured as 100 S cm⁻¹. H₅IO₆ oxidant produces first IO₃⁻ and then I₂. Therefore, it could ensure both oxidation of aniline by IO₃⁻ and then doping polyaniline with I₂, without any residual oxidant contamination. I₂, which is a well known extrinsic dopant, was produced intrinsically in this study. Thus, H₅IO₆ was found to be an effective oxidant material for the chemical polymerization of aniline.     

Electrical properties of 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl] benzene

The increase of the electrical conductivity of the arylenevinylene (AV) system 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl] benzene was measured as a function of the doping level of iodine. Compressed powders and films blended with polystyrene (PS) containing up to 30 wt.% of the oligomer were used. At the highest doping level the conductivity of the compressed powder reaches a value of 3.3×10⁻⁴ Ω⁻¹ cm⁻¹. The conductivity, measured between 90 and 300 K on the powder with the highest conductivity, is thermally activated with an activation energy of ∼0.1 eV. The thermopower is positive in agreement with a charge transfer from the organic chain to an iodine atom. Its value is small (25 μV K⁻¹) and temperature independent. The results are interpreted in terms of small-polaron hopping.     

The effect of iodine content and specimen orientation on stress corrosion crack growth rate in Zircaloy-4

The influence of specimen orientation, stress intensity factor (K_I), and iodine concentration on the iodine-induced stress corrosion cracking growth rates in Zircaloy-4 was investigated in iodized methanol solutions at ambient temperature. When K_I is lower than 20 MPa.m^1/2, the intergranular and mixed intergranular/transgranular crack propagation rates increase linearly with (K_I − K_I,th), K_I,th being the onset of propagation stress intensity factor. The increase in iodine content induces an increase of the crack growth rate for a given K_I, and a decrease of the K_I,th. The specimen orientation is a second order parameter. A crack propagation law, depending on iodine content, is proposed.     

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.     

Transmembrane redox reactions through polyaniline membrane doped with fullerene C60

Polyaniline (PANI)-C₆₀ membranes were chemically synthesized with fullerene C₆₀ content of 0.2, 0.5, 1, 2 and 3 mol% (relative to aniline fragment) respectively, and then systematically characterized with FTIR, field emission scanning electron microscopy (FESEM), XPS and electrochemical impedance spectroscopy (EIS). It is demonstrated that electron/ion coupled transport across PANI-C₆₀ membrane is possible in the presence of oxidizing agent at one side of the membrane and reducing agent at the other side. If 0.05 M acidic solution of FeCl₃ was used as the oxidizing agent and 0.3 M ascorbic acid as the reducing agent, a typical value of transmembrane transport rate of redox equivalents was 3.1 × 10⁻⁸ mol s⁻¹ cm⁻² with the membrane containing 0.5% C₆₀. This value was one order higher than that for HCl doped PANI membrane at identical conditions, which can be explained by superimposed C₆₀ doping and acid doping. The 0.5% content of C₆₀ is optimal and at higher content the rates of transmembrane redox transport decrease.     

The synthesis of low crystallinity polyacetylene from the precursor polymer polybenzvalene

The synthesis and properties of the conductive polymer precursor polybenzvalene (PBV) and its conversion to polyacetylene (PA) are presented. PBV was synthesized by ring-opening metathesis polymerization (ROMP) of benzvalene (BV) with non-Lewis acidic tungsten alkylidene catalysts. Treatment of PBV with solutions of HgCl₂, HgBr₂, ZnI₂ and AgBF₄ results in a CC bond rearrangement, and produces polyacetylene PA. The PA films produced with HgCl₂ displayed the highest conductivities and the best mechanical properties. The PA produced was of low crystallinity and upon treatment with I₂ exhibited conductivities of 1 Ω⁻¹cm⁻¹. Oriented PA was produced by stretching the PBV and converting it to PA. With I₂ doping, the oriented PA (l/l₀=6) displayed a conductivity of 49 Ω⁻¹cm⁻¹.     

Effect of ZrO2 content on microstructure and mechanical properties of W alloys fabricated by spark plasma sintering

The ultra-fine-grained ZrO₂-reinforeced W composites were obtained by hydrothermal synthesis method and spark plasma sintering. The precursors of WO₃ and Zr(OH)₂ were evenly mixed in aqueous solutions via the liquid-liquid doping, a hydrothermal method. The addition of ZrO₂ could significantly refine W particles, and thus the ultra-fine and well-mixed W-ZrO₂ composite powders were obtained after reduction, with the average size of 2 μm for W particles and ~20 nm for Y₂O₃-stabilized ZrO₂ particles. The relative density of the sintered samples increases from 92.8% to 98.9% with increasing ZrO₂ content. The W-1.5wt%ZrO₂ alloy possesses the prominent properties of 538.8 HV for microhardness, and 1628 MPa for compressive strength when compressed to 21% strain-to-failure at room temperature and a strain rate of 1.7 × 10⁻³ s⁻¹. The high temperature compressive tests shows that the existence of peak stress is not observed in the true stress-stain curves, indicating that the dynamic recovery is the main cause of deformation softening during deformation.