Modified conformation and physical properties in conducting polymers due to varying conjugation and solvent interactions

Small angle X-ray scattering (SAXS) studies of poly2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with varying conjugation, and polyethylene dioxythiophene complexed with polystyrene sulfonate (PEDOT-PSS) in different solvents have shown the importance of the role of pi-electron conjugation and solvent-chain interactions in controlling the chain conformation and assembly. In MEH-PPV, by increasing the extent of conjugation from 30 to 100%, the persistence length (l(p)) increases from 20 to 66 angstrom. Moreover, a pronounced second peak in the pair distribution function has been observed in the fully conjugated chain, at larger length scales. This feature indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. In the case of PEDOT-PSS, the chains undergo solvent induced expansion and enhanced chain organization. The clusters formed by chains are better correlated in dimethyl sulfoxide (DMSO) solution than water, as observed in the scattered intensity profiles. The values of radius of gyration and the exponent (water: 2.6, DMSO: 2.31) of power-law decay, obtained from the unified scattering function (Beaucage) analysis, give evidence for chain expansion from compact (in water) to an extended coil in DMSO solutions, which is consistent with the Kratky plot analysis. The mechanism of this transition and the increase in dc conductivity of PEDOT-PSS in DMSO solution are discussed. The onset frequency for the increase in ac conduction, as well as its temperature dependence, probes the extent of the connectivity in the PEDOT-PSS system. The enhanced charge transport in PEDOT-PSS in DMSO is attributed to the extended chain conformation, as observed in the SAXS results.

1H-4,1,2-Benzothiadiazines from 1,2,3-Benzothiadiazole via Alkylbenzothiadiazolium Salts: A Novel Heterocyclic Ring Expansion Possibly via Nitrogen Ylides.

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Anomalous X-ray scattering study of local structures in the superionic conducting class (CuI)(0.3)(Cu2O)(0.35)(MoO3)(0.35)

The anomalous X-ray scattering (AXS) method using Cu and Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (CuI)(0.3)(Cu2O)(0.35)(MoO3)(0.35). The possible atomic arrangements in near-neighbor region of this glass were estimated by coupling the results with the least-squares analysis so as to reproduce two differential intensity profiles for Cu and Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be 6.1 at the distance of 0.187 nm. This implies that the MoO6 octahedral unit is a more probable structural entity in the glass rather than MoO4 tetrahedra which has been proposed based on infrared spectroscopy. The pre-peak shoulder observed at about 10 nm(-1) may be attributed to density fluctuation originating from the MoO6 octahedral units connected with the corner sharing linkage, in which the correlation length is about 0.8 nm. The value of the coordination number of I- around Cu+ is estimated as 4.3 at 0.261 nm, suggesting an arrangement similar to that in molten CuI.

Conductivity and structural studies on disordered amorphous conducting carbon films

Amorphous carbon films are prepared by the pyrolysis of Tetra Chloro Phthalic Anhydride (TCPA) at different temperatures (700 degrees C to 900 degrees C). DC Conductivity measurements are done on the films in the temperature range 300K to 4.2K. It shows an activated temperature dependence with a small activation energy (0.02eV to 0.003eV). Variable range hopping is observed at low temperatures. The films are characterised by XRD, SEM, TEM, AFM and microRaman. The electronic structure of the film is used to explain the electrical behaviour.

Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 x 10(-2) Omega cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide. (C) 2011 Elsevier B.V. All rights reserved.

Structure of highly conducting amorphous carbon

We report on neutron diffraction study of a new form of conducting amorphous carbon up to Q similar to 14.5 Angstrom(-1). The bond distances from first two peaks in g(r) are 1.45 and 2.49 Angstrom, very similar to those in sputtered truly amorphous carbon films (Li and Lannin, Phys. Rev. Lett. 65 (1990) 1905). The first coordination number is 3.1 (+/- 0.1) indicating predominantly sp(2) hybridisation (ideal no. = 3). However, S(Q) itself shows vestiges of (0 0 2), (1 0) and (1 1) peaks, typical of glassy carbon (Mildner, J. Non-Cryst. Solids 47 (1982) 391). (C) 1998 Elsevier Science B.V. All rights reserved.

Local environmental structures of Mo in the superionic conducting glass (AgI)(0.6)(Ag2MoO4)(0.4) by anomalous X-ray scattering

The anomalous X-ray scattering (AXS) method using Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (AgI)(0.6)(Ag2MoO4)(0.4). The possible atomic arrangements in the near-neighbor region of this glass were estimated by coupling the results with the least-squares variational analysis so as to reproduce the differential intensity profile for Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be about 4 at the distance of 0.180 mn. This implies that the most probable structural entity in the glass is the MoO4 tetrahedral unit which has been proposed based on infrared spectroscopy. The value of the coordination number of I- around Ag+ is estimated as 4.4 at 0.287 nm, suggesting an arrangement similar to that of crystalline or molten AgI.

Phase modification of ammonium nitrate by potassium salts

Modification of the room temperature phase (IV-III) of ammonium nitrate (AN) has been attempted using a variety of potassium salts namely, KF, KCl, KI, KNO3, K2CO3, K2SO4, KSCN and K2Cr2O7. No phase transition was observed when AN containing 1-2% by mass of these potassium salts is heated from room temperature (25 degrees C) onwards in DTA and DSC scans, but the linear expansion due to phase transition was still observable in TMA measurements. Complete arrest of the linear expansion occurs only when a higher concentration of the additive is used. Similarly, in thermal cycling experiments, complete phase modification in the temperature range -80 to 100 degrees C occurs only with a higher percentage of the potassium salt. The extent of modification, however, is found to be dependent both on the concentration, and the type of the anion. Potassium dichromate when used as an additive modifies the phase as well as the decomposition pattern of AN.

The onset of oscillatory Marangoni convection in a two-layer system of conducting fluid in the presence of a uniform magnetic field

A combination of numerical and analytical techniques is used to analyse the effect of magnetic field and encapsulated layer on the onset of oscillatory Marangoni instability in a two layer system. Oscillatory Marangoni instability is possible for a deformed free surface only when the system is heated from above. It is observed that the existence of a second layer has a positive effect on Marangoni overstability with magnetic field whereas it has an opposite effect without magnetic field.

Correlated conformation and charge transport in multiwall carbon nanotube-conducting polymer nanocomposites

The strikingly different charge transport behaviours in nanocomposites of multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylenedioxythiophene-polystyrene-sulfonic-acid (PEDOT-PSS) at low temperatures are explained by probing their conformational properties using small-angle x-ray scattering (SAXS). The SAXS studies indicate the assembly of elongated PEDOT-PSS globules on the walls of nanotubes, coating them partially, thereby limiting the interaction between the nanotubes in the polymer matrix. This results in a charge transport governed mainly by small polarons in the conducting polymer despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge carriers following one-dimensional variable range hopping is evident which also gives rise to a positive magnetoresistance (MR) with an enhanced localization length (similar to 5 nm) due to the presence of MWNTs. However, at T < 4 K, the observation of an unconventional positive temperature coefficient of resistivity is attributed to small polaron tunnelling. The exceptionally large negative MR observed in this temperature regime is conjectured to be due to the presence of quasi-1D MWNTs that can aid in lowering the tunnelling barrier across the nanotube-polymer boundary resulting in large delocalization.

Synthesis of electrically conducting copolymers of aniline with o/m-amino benzoic acid by an inverse emulsion pathway

Copolymers of aniline and ortholmeta-amino benzoic acid were synthesized by chemical polymerization using an inverse emulsion pathway. The copolymers are soluble in organic solvents, and the solubility increases with the amino benzoic acid content in the feed. The reaction conditions were optimized with emphasis on high yield and relatively good conductivity (2.5 X 10(-1) S cm(-1)). The copolymers were characterized by a number of techniques including UV-vis, FT-IR, FT-Raman, EPR and NNM spectroscopy, thermal analysis, SEM and conductivity. The influence of the carboxylic acid group ring substituent on the copolymers is investigated. The spectral studies reveal that the amino benzoic acid groups restrict the conjugation along the polymer chain. The SEM micrographs of the copolymers reveal regions of amorphous and crystalline domain. Thermal studies indicate a marginally higher thermal stability for poly(aniline-co-m-amino benzoic acid) compared to poly(aniline-co-o-amino benzoic acid). (C) 2002 Elsevier Science Ltd. All rights reserved.

Electrical and optical characterization of conducting polymers by THz time-domain spectroscopy

The absorption and index of refraction of polypyrrole (PPy) and poly-3-methylthiophene (PMeT), from low frequencies up to 4 THz, have been measured by tera-Herz (THz) time-domain spectroscopy. The complex conductance was obtained over this range of frequency. Highly conducting metallic samples follow the Drude model, whereas less conducting ones fit the localization-modified Drude model. The carrier scattering time and mobility in conducting polymers can be directly determined from these measurements.

Synthesis of electrically conducting copolymers of o-/m-toluidines and o-/m-amino benzoic acid in an organic peroxide system and their characterization

Copolymers of o-lm-toluidine with o-lm-amino benzoic acid have been synthesized by chemical polymerization using inverse emulsion pathway and characterized by a number of techniques including UV-Vis, FT-IR, FT Raman, EPR and NMR spectroscopies, thermal analysis and conductivity. The solubility of the copolymers in organic solvents increases with increase in the amount of amino benzoic acid in the feed. The copolymers synthesized at room temperature show relatively higher conductivity and are obtained in higher yield compared to those synthesized at 0 and 60 degreesC. The spectral studies have revealed restricted conjugation along the polymer chain. The effect of -COOH substituent on the copolymer structure is discussed. (C) 2003 Elsevier Science B.V All rights reserved.

Physical chemistry of mixed conducting zirconia ceramics

Suivant la pression partielle d'oxygène, la zircone peut être conducteur ionique ou électronique. Mise au point de méthodes de mesures de f.é.m. permettant de s'affranchir des sources d'erreur introduites par ces propriétés.