Thermally Stimulated Discharge Current Peak Research Articles

Measurement of AC and DC relaxation properties in polyvinyl chloride (PVC) nanocomposites

In present investigation, thin film of polyvinylchloride (PVC)/silicon dioxide (SiO2)/montomorillonite (MMT) nanocomposites were prepared by solution casting method. AFM analyzed the grain size, particle size, roughness and dispersion of nanofillers in PVC nanocomposites. However, FTIR describes the molecular interaction of nanofillers in PVC structure. The AC and DC relaxation properties of these nanocomposites were measured by means of dielectric spectroscopy and thermally stimulated discharge current (TSDC) respectively. The dielectric spectroscopy has been applied to measure dielectric constant and tangential loss at different frequencies and temperatures; then, it has been specified the effectiveness of nanoparticles on dielectric performance as compared with pure PVC. The permittivity of these nanocomposites is enhanced remarkably, which can be understood by the interfacial polarization effect. The high dielectric constant of value 37 is obtained in the nanocomposite with 4 wt.% MMT at 50 Hz. The temperature dependent dielectric constant could be explained on the basis of free volume available for free charge carriers and MWS relaxation process. The dielectric characteristics are highly influenced by nature of fillers and can be understand by the frequency and temperature dependence of the interfacial relaxation. TSDC peaks are originated due to α-relaxation process and MWS relaxation process.

Measurement of thermally stimulated discharge current (TSDC) for detection of thyroid-stimulating hormone (TSH) in human blood

TSDC was measured in human blood sample with different level of TSH. The origin of TSDC could be explained on the basis of bioelectret effect in biological sample, which is interpreted by fundamental concepts of bioelectret state in biopolymers. The concept of thermal analysis of blood gives the basis of TSDC peaks. The nature of the TSDC peaks and their relation to the physicochemical transformations and the interphase interactions in these systems are discussed. It is observed that the position of TSDC peak is different for different level of TSH. The activation energy, charge released, and peak current were observed to decrease with TSH contents in human blood. The increase of TSH nonpolar salt in human blood is associated with the decrease of charge carriers due to denaturation or hydration of protein with temperature. It is noted that TSDC can be suitable diagnostics of TSH in human blood.

Thermally stimulated discharge current (TSDC) characteristics in β-phase PVDF–BaTiO3 nanocomposites

β-phase polyvinylidene fluoride (PVDF)–BaTiO3 nanocomposite samples have been prepared by solution mixing method. XRD data represent that the crystallinity of PVDF decreases with increase in loading level of BaTiO3 nanoparticles. DSC curve represents that the melting point of PVDF is lightly affected by loading concentration of BaTiO3. The morphology and microstructure of PVDF and PVDF embedded by BaTiO3 nanofillers were investigated by using inverted contrast microscopy (ICM) and scanning electron microscopy (SEM). FTIR interferrometry is proven that PVDF and BaTiO3 are not chemically interacting; therefore, interaction of BaTiO3 is van der Waals type of interaction. The thermally stimulated discharge current (TSDC) of PVDF and PVDF–BaTiO3 nanocomposites sample was characterized by single peak. The observed TSDC peak is discussed on the basis of dipolar and interfacial polarization.

Study of trap structure of thermally polarized polyimide

The trap structure of polyimide was studied using open-circuit thermally stimulated discharge current (TSDC). TSDC was observed in 25-μm thin film of polyimide at different condition of polarizing field and temperature. The one-sided vacuum-aluminized samples were used to record the open-circuit thermally stimulated current. The dipolar mechanism of relaxation is a possible mechanism to explain the behavior of TSDC peak at low temperature and field condition; however, hopping transport mechanism is prominent for the sample polarized with higher field and temperature. This is because deeper traps capture the charge carriers at high polarizing field and temperature and their subsequent trapping through hopping process. The influence of surface traps is caused by thermal polarization; it is evident due to lower value of activation energy, since activation energy of TSDC peak is corresponding to surface traps. The morphology of surface traps is verified by measuring the surface roughness using atomic force microscopy. The both type of charges (i.e., heterocharge and homocharge) are responsible for flow of current in presence of air gap. We report the role of surface and deep traps induced due to charging process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Investigation of thermally stimulated charge relaxation mechanism in SiO2 filled polycarbonate nanocomposites

Abstract The thermally stimulated charge relaxation properties of polycarbonate (PC) filled with SiO2 nanofiller were studied by means of thermally stimulated discharge current (TSDC). The nanocomposite samples were further characterized by UV–vis spectroscopy, scanning electron microscopy, energy dispersive X-ray spectra, and differential scanning calorimetry (DSC) techniques to investigate the dispersion of nanofillers in polymer matrix and glass transition temperature. All pristine and nanocomposites samples of thickness about 25 μm were prepared using solution mixing method. The suitable weight percentage of SiO2 nanofillers has been chosen to prevent the nonuniform dispersion. TSDC measurement of PC (Pristine) and PC+ (7% SiO2) shows the single peak, while TSDC characteristic of other nanocomposites are showing two peaks. The higher temperature TSDC peak of pristine and nanocomposites samples is originated due to the charge relaxation from shallower and deeper trapping sites, however, low temperature...

Optical and thermo electrical properties of ZnO nano particle filled polystyrene

AbstractThe study of optical and thermally stimulated electrical properties such as optical band gap, refractive index, X‐ray spectra, SEM spectra, thermally stimulated discharge current (TSDC), differential scanning calorimetry (DSC) have been undertaken in ZnO nanoparicle filled polystyrene nanocomposite thin film of 30 μm thickness. The appearance of single TSDC peak at temperature 408 ± 5 K in nanocomposite samples shows the charge carriers injected from deeper trapping levels. It is due to the modification of surface and bulk properties of polystyrene by filling of ZnO nanoparticles. In other hand, the strong interaction of nanoparticles with polymer matrix is the expected reason of improvement of crystallite size, optical energy band gap, refractive index, TSDC, glass transition temperature, and charge storage. It is confirmed from SEM images that the modifications of these properties are caused by creation of clusters in amorphous–crystalline boundaries of pristine polystyrene. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Thermally stimulated current and differential scanning calorimetry spectroscopy for the study of polymer nanocomposites

The thermally stimulated discharge current (TSC) and differential scanning calorimetry (DSC) spectroscopy have been recorded in 25 μm thick samples of pristine polycarbonate (PC) and zinc oxide nano particle-filled polycarbonate. Polycarbonate (PC)/zinc oxide (ZnO) nanocomposites of different mass ratio (e.g., 1, 3, and 5%) were prepared by sol–gel method, followed by film casting. The glass transition temperature of nanocomposite samples increases with increase in concentration of ZnO nano fillers. It is due to the strong interaction between inorganic and organic components. The TSC peaks of nanocomposite and pristine PC indicate the multiple relaxation process. It has been observed that the magnitude of TSC decreases with increase in concentration of nanofillers. The TSC characteristics of 5% filled nanocomposites shows exponential increase of current at higher temperature region. This increase in current is caused by formation of charge-transfer complex between inorganic phase (e.g., ZnO) and organic phase (e.g., PC). Thus, the nano material like zinc oxide transfers the charge carriers from inorganic phase to organic phase rapidly and resultant current increases exponentially. This current is known as leakage current or breakdown current. TSC peak height is observed as a function of the polarizing field. The height of TSC peak increases as the field increases in pristine PC, while TSC peak height is suppressed in nanocomposite samples. This indicates the amount of space charge is smaller in the nanocomposites with a proper addition of ZnO nano fillers than in the pristine PC.

Relaxation investigations in polysulfone: Thermally stimulated discharge current and dielectric spectroscopy

The temperature and electric field dependence of dielectric relaxation have been investigated in amorphous polysulfone (PSF) samples using thermally stimulated discharge current (TSDC) and AC dielectric measurement. All measurements were performed on solution grown thin films of thickness 50 μm. The nature of relaxation mechanisms in amorphous PSF is discussed on the basis of TSDC and dielectric measurement results. The comparative studies of dielectric properties with TSDC indicated a strong resemblance between the two techniques. Polysulfone (PSF) films are characterized by two TSDC peaks, i.e. β peak at 348 K and α peak at 470 K. The depolarization current for the β peak increases linearly with poling field. The peak obtained at lower temperature (i.e. β peak) is associated with dipolar relaxation and the other one obtained at high temperature (i.e. α peak), which appears due to the α relaxation.

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.

Space- and surface-charge analysis of plasma-preprocessed PTFE thin films

The space- and surface-charge behavior of corona-charged polytetrafluoroethylene thin films after plasma processing were studied experimentally by space-charge density distribution measurement and thermally stimulated discharge current (TSDC) measurement. The effect of the antistatic process using low-pressure discharge plasma and charge elimination process dipping in tap water was examined. The surface composition of the samples which were plasma- processed was analyzed with X-ray photoelectron spectroscopy (XPS) to study the mechanisms of antistatic process. It was found that charge elimination of plasma-processed samples was enhanced, independently of the kind of processing gas during the plasma processing. Oxygen and nitrogen atoms were observed from the XPS measurement of plasma-processed samples. In particular, a large amount of nitrogen atoms was found on the surface of the samples plasma processed in pure nitrogen gas. The samples plasma processed in pure nitrogen gas showed a large hetero TSDC peak at room temperature before the charge-elimination process. This might be due to nitrogen atoms on the sample surface that were generated during plasma processing.

Electret behaviour of ion irradiated polycarbonate and kapton-H polyimide films

The electret state of a polymer arises from the induced polarization owing to the frozen in phenomenon of electric charges. The study of electret nature using thermally stimulated discharge current (TSDC) technique reveals the nature of various relaxation processes in a polymer. When a polymer is irradiated with high energy ions their dielectric relaxations get affected which can be investigated using above mentioned technique. Reported here are the results of TSD current spectra of films of polycarbonate (PC) (irradiated with 100 MeV Ag +, flux; 1 × 10 11 and 1 × 10 9 ions/cm 2) and kapton-H polyimide (irradiated with 100 MeV O ++, flux; 1 × 10 5 ions/cm 2). The as-received and irradiated samples of PC were polarised at 120 °C using a 200 kV/cm electric field while those of kapton-H were polarised at 90 °C, field; 133 kV/cm and 180 °C, field; 266 kV/cm. With PC it is observed that the irradiation does not affect the location of TSDC peak occurring at 144 °C (activation energy; 0.6 eV); however, the peak magnitude changes with irradiation dose. The peak being associated with dipolar relaxation the ion-irradiation seems to have changed the number of dipoles. The high temperature TSDC spectra is however largely affected by irradiation giving evidence of the presence of new traps. With kapton-H, it is observed that TSD current changes its direction (anomalous TSDC) in irradiated samples in the high temperature region. Such behaviour has not been observed in the thermoelectrets of as-received samples. Only the corona charged electrets were observed to give such anomalous TSDC behaviour. This suggests the creation of new energy traps from irradiation. The bulk nature of this relaxation is confirmed by the TSDC of repoled samples. The irradiation induced shallow energy traps along with dipolar relaxation are also observed from the TSDC spectra in the low temperature region.

Transient and thermally stimulated depolarization currents in polyvinyl formal films

AbstractTransient currents in double‐sided vacuum aluminized polyvinyl formal (PVF) film samples of thickness 40 μm were investigated in the charge and discharge modes at different temperatures and fileds. The results observed suggest that the transient currents are governed by charge injection processes leading to space charge effects. Comparative studies of the isochronal characteristics (i.e. current–temperature plots at fixed times) with the thermally stimulated discharge current (TSDC) indicated a strong resemblance between the two techniques. These studies suggest that the simultaneous mechanism of movement of charges through microscopic distances coupled with dipolar orientation may be responsible for the TSDC peak observed at 100°C.

Changing of HDPE film due to surface effects during fabrication

Abstract High density polyethylene (HDPE) films have been fabricated using a presse-sheet system. The results of thermally stimulated discharge current (TSDC) analysis on these films are presented. The relationship between TSDC results and film manufacturing parameters are also presented. The following are the parameters investigated; cooling rate, film forming pressure and surface roughness. The surface roughness is shown to be dependent on the “forming plate” material. These materials investigated are Teflon TM , stainless steel and aluminum. Using Teflon TM as the forming plate causes the HDPE film to display a large TSDC homocurrent peak at 120°C. However, using stainless steel as the forming plate causes the HDPE film to display no TSDC peaks. Results of the characterization of HDPE surfaces immediately following the peeling of the forming plate materials are presented. Results of the characterization of plasma treated surfaces are presented before and after a second treatment using a low pressure glow discharge.

Application of thermally stimulated discharge techniques to a-Se: Te/Se double-layer photoreceptors

Interface traps in a-Se:Te/Se double-layer xerographic photoreceptors were studied using thermally stimulated discharge (TSD) techniques. Two peaks are found in the TSD current curve which are believed to be due to two distinctly different types of space charge polarization. The well-defined low-temperature peak is centred at approximately −8 °C and it is due to the difference in the dielectric constants and electrical conductivities of a-Se:Te and a-Se layers. It is argued that on the application of an electric field with positive polarity applied to the a-Se:Te layer, the Maxwell-Wagner effect causes the build up of a positive (holes) space charge layer at the interface of the two layers. The observed TSD current peak seems to be dominated by the neutralization currents in the a-Se:Te layer. The broad high-temperature peak occurs between 30 and 50 °C in the thermograms and it is believed to be due to release of holes from the deep traps at the interface between the two layers. The density of these traps is estimated to be ∼1010 cm−3. The activation energy relaxation corresponds to the effective energy for the detrapping of holes from the interface states and is calculated to be ∼ 0.54 eV.

Dopant concentration effect on the thermal discharge behaviour of Fe-doped polyvinyl acetate films

The thermal discharge behaviour of pure and Fe-doped polyvinyl acetate films under different conditions has been studied using the TSDC (thermally stimulated discharge current) technique. The peak positions, peak currents, stored charge and activation energies associated with the TSDC peaks are strongly affected by the concentration of the dopant. The results have been explained in terms of the interaction between the dopant (Fe) and acetate group in the polymer matrix.

On the nature of AC field aging of cross-linked polyethylene using liquid electrodes

The nature of AC field (6 kV mm-1 and 1 kHz) aging of cross-linked polyethylene (XLPE) with (i) NaCl and (ii) CuSO4 (0.1 M) liquid electrodes has been studied with thermally stimulated discharge current (TSDC), thermal transient current (TTC) and Fourier transform infrared spectroscopic (FTIR) techniques. The behaviour of thermal transient current appears to be related to the electrical aging time and consists primarily of two components, i.e. dipolar and space-charge contributions. The magnitude of the TTC is related to that of the integrated charge released in a TSDC thermogram. FTIR measurements show that oxidation of stabilized XLPE is significantly lower than that of the unstabilized polymer. No noticeable increase in bound water content in the polymer was observed as measured by IR absorbance at approximately 3370 cm-1. Progressive enhancement of absorbance at approximately 1715 cm-1 and the TSDC peak at 70 degrees C with increasing field aging time appear to have the same origin.

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.

Effect of copolymerization with chloranil on the polarization processes in polystyrene

Polarization processes in polystyrene-chloranil copolymer have been investigated by the thermally stimulated discharge (TSD) technique. The observed TSD current peak consists of contributions from two different processes having activation energies 0.78 and 1.29 eV. The single peak could not be resolved into its constituents due to experimental limitations. Comparison of the TSD results for the copolymer with those of pure polystyrene and chloranil suggests that dipolar and space charge types of polarization are playing a role in the polarization of the copolymer.

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.