Thermally stimulated discharge current studies of acrylic-acid-doped polystyrene films

Thermally stimulated discharge currents in thin cylindrical films (30 μm thick) of polystyrene either undoped or doped with acrylic acid were measured under various polarizing conditions. It was found that the undoped samples give rise to a single peak around 105 °C which is due to the release of space charges present in the material. In the doped samples this peak is shifted to 58 °C and another peak appears at around 150 °C. The peak at the lower temperature is due to the superposition of the dipolar peak of the dopant and the space-charge-limited peak of the matrix, whereas the peak at the higher temperature has been attributed to the space charge of the material retained in the double bonds of the dopant, as a result of interaction between the dopant and the matrix.     

Thermally stimulated discharge currents in polyvinyl pyrrolidone polymer films

Polyvinyl pyrrolidone films of thickness 17.6 μm were grown by the isothermal solution growth technique. Thermally stimulated discharge currents were studied on these films as a function of polarizing field strength and polarizing temperature, at a constant heating rate of 0.14 Ks⁻¹. In all these studies only one TSDC peak was observed and the temperature corresponding to this peak was found to show weak but definite dependence on the polarizing field strength and polarizing temperature. The activation energies and relaxation parameters and charge associated with this peak were evaluated. The origin of TSDC was attributed to the space charge process.     

Thermally stimulated discharge current studies on PMMA-PVAc blends

Thermally stimulated discharge current (TSDC) studies have been carried out on blends of polymethyl methacrylate (PMMA) and polyvinyl acetate (PVA). The effects of polarization temperature and field on the TSDC peaks of polyblends indicate that the polarization in the polyblends is due to charge-carrier trapping in deep traps which leads to induced dipole formation. The results of a.c. dielectric bridge measurements are also compared with the TSDC results. The dielectric relaxation parameters are also reported.     

Thermally stimulated discharge currents in iodine-doped polystyrene films

Studies were made of the thermally stimulated discharge (TSD) current in iodine-doped polystyrene (PS) films (20 μm thick) as a function of the iodine concentration and the temperature of polarization. Unpolarized doped films were observed to give TSD currents. This is attributed to the formation of charge transfer complexes (CTCs) between iodine and the main molecular chain of PS. Doping PS with iodine lowers the temperáture at which the current peak occurs and enhances the peak current. An increase in the temperature of polarization increases the TSD current and shifts its maximum to a higher temperature while an increase in the concentration of iodine lowers the activation energy of the discharge process. The thermally assisted detrapping of carriers is suggested as a possible mechanism.     

Thermally stimulated discharge currents from pyrene-doped polystyrene films

Pyrene was mixed with polystyrene (PS) in different molar concentrations in the range 0.2–12 mol.% and thermally stimulated discharge (TSD) current spectra of the doped PS films were studied for various dopant concentrations, polarizing fields and forming temperatures. Unpolarized films were observed to give a peak at 95°C. The TSD current peak in the main relaxation region of PS shifts to the lower temperature side of the spectrum with increasing concentration of the dopant. The strong dependence of space charge polarization on the dopant concentration and the forming temperature is assigned to an increase in the conductivity of the polymer.     

Thermally stimulated discharge conductivity in polymer composite thin films

This paper describes the results of thermally stimulated discharge conductivity study of activated charcoal-polyvinyl chloride (PVC) thin film thermoelectrets. TSDC has been carried out in the temperature range 308–400°K and at four different polarizing fields. Results are discussed on the basis of mobility of activated charcoal and polyvinyl chloride chains.     

Thermal and IR studies on copper doped polyvinyl alcohol

5 mol% PVA: x mol% Cu²⁺ polymer films were prepared by casting process. Thermal transitions and thermal degradation of samples with respect to copper concentration were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Increase in glass transition temperature as a function of copper concentration shows a strong branching and steric effects in copper doped PVA complexes. Thermal degradation of films to an extent of 4–5% was found with an increase in copper content. FTIR spectrum of PVA doped Cu²⁺ ions indicate the presence of O-H, C-H, C=C and C-O groups.     

Thermally stimulated current study in polyvinyl chloride (PVC)-mica composites

Mica powder was dispersed in polyvinyl chloride (PVC) in different percentages by weight and the thermally stimulated discharge current of the composites was studied. The results are discussed in terms of dipolar and space charge polarization that leads to induced dipole formation. Activation energies have been calculated for all the samples by the initial rise method.     

Electron paramagnetic resonance and optical absorption studies of Cu2+ ion doped polyvinyl alcohol films

Electron paramagnetic resonance (EPR) and optical absorption studies have been carried out on Cu²⁺ ions doped in polyvinyl alcohol films (PVA). EPR spectrum at room temperature exhibits hyperfine structure characteristic of Cu²⁺ ions in tetragonal symmetry. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy is calculated. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures and the Curie constant is evaluated from 1/χ versus T graph. The optical absorption spectrum exhibits a broad band which has been assigned to the transition ²B_1g → ²B_2g.     

Thermally stimulated discharge current (TSDC) and dielectric constant of semiconducting glasses

In this paper the results of thermally stimulated discharge current (TSDC) and dielectric constant for 40PbO-60Bi₂O₃ glass thermoelectrets are presented. Measurements of TSDC and dielectric constant, ǵe, have been carried out in the temperature range 30–300°C. The thermoelectrets were prepared at different polarizing fields. The various observed peaks in the thermograms are discussed on the basis of space charge polarization. The trap energy is evaluated from the Garlick-Gibson plot of initial rise method. Similarly other parameters such as relaxation time, charge release etc are evaluated.     

Thermally stimulated discharge current and DC resistivity of ethylene propylene rubberwith various Pb concentrations

DC resistivity of extruded ethylene propylene rubber (EPR) samples with various Pb concentration have been measured under wet conditions as a function of electrical field at selected temperatures in a range from 20 to 100°C. The temperature and electrical field coefficients of resistivity have been calculated. Thermally stimulated discharge current (TSDC) has also been measured and a broad positive peak has been observed for three EPR samples. It has been found that the resistivity of EPR is not sensitive to the Pb concentration within the range of 0 to 5 parts per hundred base resin (phr). The results show that the resistivity of EPR varies non-linearly with both temperature and electrical field. The temperature coefficient of resistivity α of EPR has been measured to be ∼0.1 K⁻¹ for all the samples with various Pb concentration. The electrical field coefficient of resistivity β of EPR at room temperature is small and increases with temperature. Increasing Pb content increases slightly the electrical field coefficient β of resistivity. Based on a space charge limited conduction model, the trap depth of EPR has been estimated. TSDC measurements indicate that doping with Pb increases both the density of charge carriers and the number of deep traps simultaneously. The broad TSDC peak reveals that there must be a distribution rather than just a single value of the trap depth.     

Thermally stimulated current changes of irradiated skin

Radiation effects on collagen and skin have been characterized by means of thermally stimulated current (TSC) spectroscopy. X-rays, -rays and UV radiation have similar effects on the molecular mobility of dermal collagen and skin. They induce a decrease of intra and intermolecular mobility. The restriction of molecular movement can be explained by an increase of collagen cross-links.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Thermally stimulated discharge currents in corona-charged aramid paper

Thermally stimulated discharge (TSD) currents were measured in corona-charged aramid paper to study the mechanisms of charge storage and its subsequent release from the bulk of the material. Studies were carried out on paper thicknesses of 76 and 127 m using a point-plane gap in air at atmospheric pressure. TSD currents were measured over a temperature range of 0–200 °C and the influence of various parameters, such as the poling voltage, rate of heating and effect of electrode materials, were investigated. Corona-charged aramid paper with positive polarity voltage showed that the TSD current is of either polarity depending upon the temperature range. Three distinct peaks were observed, one in the low-temperature range, 20–25 °C, and the other two peaks at higher temperatures. The low-temperature peak was considered to be due to an abnormal TSD current, whereas the currents at higher temperatures were normal TSD currents. Activation energies were determined using the low-temperature tail of the TSD curves and were found to be dependent on extrinsic parameters such as the thickness of the sample. The activation energy for aluminium electrodes was observed to be in the range of 0.5–2.0 eV. The TSD currents for the low-temperature peak was considered to be electronic. It is postulated that the charge carriers are generated within the material by the intense electric field due to corona.     

Thermally stimulated polarization current in sodium germanate glass

The electrical conductivity of XNa₂O·(100–X)GeO₂ glasses where X is 0.19 and 27.5 mol%, was studied by means of the technique of thermally stimulated polarization current. The compositional dependence of the parameter ₀ T/n ^1/3, where ₀ is the preexponential facor for conductivity and n is the nominal concentration of sodium ions, suggests that these glasses contain some sort of inhomogeneities. This suggestion is supported by the phase diagram.     

Study of optical properties of pure and MoO3-doped polyvinyl alcohol films irradiated with γ-rays

Cast thin films of pure and MoO3-doped polyvinyl alcohol (PVA) have been prepared. The optical transmission spectra in ultraviolet to near-infrared regions are investigated before and after irradiation by different doses of γ-rays in the range 102 to 107 Gy. The analysis of transmission spectra showed that the intensity of the bands is remarkably affected by both dopant concentration and γ-irradiation doses. The disappearance of the transmission band at 265 nm in 1.0 wt% and 2.0 wt% MoO3 is attributed to the structural change due to dopant. It was found that doping with molybdenum oxide results in an additional band at 600 nm. The optical energy gap and band tail of pure and MoO3-doped PVA samples at different γ-doses are estimated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermally stimulated argon release from amorphous alloy films

A new diagnostic technique is described for the study of kinetic processes in sputtered thin films. Examples are given of application to amorphous chalcogenide alloys, and are compared with the results of differential scanning calorimetry.