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MIT World Peace University

Engineering and Technology

An unusual molecular ordering, as evidenced by number and sharpness of X-ray diffraction peaks, has been observed in electrochemically synthesized conducting copolymer of pyrrole with N-phenyl maleimide. The comonomer N-phenyl maleimide is hitherto unused in the synthesis of conducting polymers. The copolymer formation has been established by X-ray photoelectron spectroscopy. As derived from wide angle X-ray diffraction data, this novel copolymer possesses an orthorhombic structure with unit cell dimensions of a=9.28 A ̊, b=7.1 A ̊ and c=8.4 A ̊. From these parameters, it is inferred that the comonomers are placed in an alternate manner maintaining isotactic stereoregular conformation. Quite interestingly, this pyrrole N-phenyl maleimide copolymer, even with the absence of extended π conjugation, exhibits electrical conductivity comparable to pyrrole homopolymer itself. © 1992.

World University root node

School of Polymer Engineering

Solid State Communications

Molecular ordering in electrochemically synthesized conducting copolymer of pyrrole with N-phenyl maleimide

The dielectric relaxation has been investigated for a segmented copolyester film containing 76% hard segments (PBT) and 24% soft tetramethylene oxide segments grown under different conditions. Distinct features have been noted in the α- and β-relaxations peaks of dielectric loss spectra depending on whether the samples were melt-grown or solution-cast. These differences have been attributed to the changes in morphology and chain configuration, especially the (CH2)4O groups, caused by the preparative technique used. © 1991.

European Polymer Journal

Effect of Morphology on the dielectric properties of a segmented copolyester

The electrical properties, namely d.c. and a.c. conductivity, of polyester elastomer filled with various metallic and ferrite fillers have been investigated as a function of temperature, frequency and filler concentration. The temperature dependence of resistivity exhibited two regions of low and high activation energy (ΔE). The value of ΔE the lower temperature region (I) decreased while in the higher temperature region (II) it increased with the increase of work function of the metal used. Only in the case of ferrite-filled composites could a positive temperature coefficient of resistance be observed. The frequency dependence of conductivity revealed that there is a very large intergranular capacitance which was even more in the case of ferrite-filled samples than in metal-filled ones. The various results have been explained on the basis of Schottky barrier formation and the depletion regions formed near the polymer-metal interface. © 1991 Chapman & Hall.

Journal of Materials Science

Electrical properties of polyester elastomer composites containing metallic fillers

The crystallinity, particle size and morphology of polyphenylene sulphide synthesized from 1, 4-dibromobenzene and sodium sulphide have been investigated by X-ray diffraction and scanning electron microscopy. It was found that the crystallinity increased from 62 to 68% with an increase in reaction time. A reordering of crystalline structure with increase of reaction time was also noted. The particle size growth was slower as compared to the reaction rate and the distribution was very sharp. The results are compared with those for polyphenylene sulphide obtained from 1, 4-dichlorobenzene and sodium sulphide. © 1990 Chapman and Hall Ltd.

Structure, growth and morphology of polyphenylene sulphide - Part 2 Effect of dibromobenzene

It is generally well known that a semiconductor is a good photoanode if it is n-type (or a good photocathode if it is p-type). This means that in the case of a photoelectrochemical (PEC) system based on an n-type semiconductor like CdS, a photoeffect (i.e. photocurrent) can be observed only under anodic polarization. However, only occasionally have there been reports in the literature which have dealt with the observation of a cathodic photocurrent for n-type CdS electrodes. Studies have been performed on n-CdS electrodes possessing a low resistivity (and practically feeble photoconductivity) in connection with PEC solar cells. Quite interestingly, we have observed this photocathodic effect while carrying out PEC evaluation of semi-insulating (i.e. highly resistive) and highly photoconductive CdS electrodes doped with Cu and Cl (henceforth referred to as CdS + CuCl electrodes). The purpose of this paper is to investigate the origin of the photocathodic effect at such a CdS + CuCl based photoconductor/ electrolyte system. Results show that there is a close link between solid-state photosensitivity and PEC currents. This is particularly evident in the cathodic case, wherein the photocurrent, i.e. photomodulated majority carrier current, flows due to a reduction in Rs, the extent of which, in turn, is determined by the solid-state photosensitivity of the samples.

Journal of Electroanalytical Chemistry

Origin of the photocathodic effect at CdS + CuCl electrodes

The doping of polymers with iodine (a strong electronic acceptor) for increasing their conductivity has been used in polyphenylene sulfide. The main drawback of this dopant is its diffusion, giving rise to instability in the electric conductivity. We found that the conductivity not only could be stabilized but also enhanced by the presence of some dyes which are known to form stable complexes with iodine. These finding with a particular emphasis on phthalocyanine are reported in this article.

Journal of Polymer Science Part C: Polymer Letters

Stabilization of high conductivity in iodine doped polyphenylene sulfide

The electrical conductivity of polyphenylene sulfide doped with ferric chloride using various solvents has been studied as a function of dopant concentration, temperature, etc. The conductivity (a) was found to increase by almost 10 orders of magnitude by using certain doping media and the the concentration (σ) dependence followed a power law of the type σ α cn where n has a value between 5.5 and 6.0. The temperature dependence of conductivity revealed two distinct regions with the activation energy having low (0.3-0.5 eV) and high (1.5-2.5 eV) values, respectively. The x-ray diffraction studies show no major changes in the crystalline structure/crystallinity even at high doping levels. These various findings have been explained on the basis of preferential diffusion of the dopant in the amorphous regions and the formation of a two-phase system.

Journal of Macromolecular Science, Part B

Semiconducting behavior of polyphenylene sulfide doped with ferric chloride

The photoelectrochemical characterisation of highly photosensitive and semi-insulating sintered pellets of CdS doped with Cu and Cl has been carried out. In the course of this work, we have observed a complete suppressin of the dark current but a pronounced photocurrent under cathodic polarisation. Both these observations indicate an unusual cathodic (i.e. forward bias) behaviour. It has been shown that due to a decrease in series resistance under illumination by an extrinsic photoconductivity effect, the “ideal” cathodic behaviour, i.e. normally found in dark for an n-CdS electrode with low resistivity, can get restored. We have also observed a red shift in the anodic photoelectrochemical spectral response of these samples. It is in agreement with our previous photoelectrochemical studies on CdS: Cu: Cl electrodes and can be explained by considering a Cu impurity excitation process. Additionally, we have observed that the background illuminations as such (employed in the “double-beam” technique of spectral response determination) do not alter the overall nature of the spectral response but result in an interesting photocurrent enhancement phenomenon. These photocurrent enhancement observations have been explained by taking into account the photoeffects at Cl-compensated Cu acceptor centers possessing a high capture cross section preferably for photoexcited holes.

Solar Energy Materials

The photoelectrochemical studies on CdS: Cu: Cl electrodes: Importance of photoconductivity effects

The characteristics of a gaseous discharge have been studied in the presence of a localised transverse magnetic field applied to a discharge tube. The breakdown voltage and the post breakdown discharge current are found to be dependent on the strength and the position of the applied magnetic field. The position of the magnetic field at which the electrical parameters of the gaseous discharge are more sensitive to the magnetic field has been identified to be very near the cathode end of the negative glow. All the experimental observations in this study have been explained consistently taking into consideration the complexity of the electrical conduction in the presence of the localised magnetic field. © 1988.

Physica B+C

Effects of localised transverse magnetic field on the characteristics of a glow discharge

The crystallinity of poly(phenylene sulphide) (PPS) blended with polystyrene has been investigated as a function of composition, annealing time and temperature by an X-ray diffraction technique for samples made by three mixing techniques viz. powder blending, melt blending and solution blending. The method of blending has a pronounced effect on the crystallinity, solution blending giving the least for a particular composition. The crystallization half time increases while the crystallite size is reduced considerably by the addition of polystyrene to PPS. These findings have been explained on the basis of partial miscibility of the amorphous phases. © 1987.