Thermally Stimulated Depolarization Current Spectra Research Articles

Sulfobetaine polyurethane ionomers. 3. Dielectric and mechanical properties of polyester polyurethane ionomer films and related compounds with Pb2+ and Co2+

AbstractTensile and dielectric relaxation properties of sulfobetaine polyurethane ionomers based on polyesters were studied comparatively to the non‐ionic polyurethane and derived compounds with Pb2+ and Co2+, using stress‐strain and thermally stimulated depolarization currents (TSDC) methods. Introduction of ionic centers into polyurethane chain improves the tensile properties and modifies the TSDC spectra. These effects are assigned to an enhancement of the microphase segregation. Complexation with Pb2+ and Co2+ diminishes the tensile properties, suggesting that an increase of phase mixing occurs determined by a partial neutralization of ionic centers. Treatment with H2S slightly increases tensile properties and changes TSDC spectra owing to the presence of the semiconducting microphases formed by clustering of the metal sulfides PbS and CoS, respectively.

Relaxation phenomena in the vicinity of the glass transition of poly (p-phenylene sulfide)

Thermally stimulated depolarization current (TSDC), thermal sampling (TS) TSDC, and dielectric spectra of poly(p-phenylene sulfide) (PPS) were measured in the vicinity of the glass transition temperature Tg. The global TSDC spectra of amorphous PPS with varying the poling temperature revealed the presence of two TSDC peaks. Only a very intense peak associated with the α relaxation (the glass transition) was observed at 367 K in the global TSDC spectra poled at above 360 K, while an additional peak was observed at around 330 K in those spectra poled at below 355 K. This additional peak observed at below Tg was considered to be originated from the secondary sub-Tg relaxation. Both the sub-Tg and the α relaxations were analyzed from elementary TSDC spectra obtained by the TS technique. It was found that the temperature dependence of the relaxation times in both relaxations was ruled by the same compensation law. The physical meaning of the compensation temperature is discussed in relation to the thermal-expansion coefficient. Moreover, the dielectric constant ε′ and dielectric loss factor ε″ of amorphous PPS are calculated using the relaxation parameters derived from the TS-TSDC analysis. Numerical results of dielectric data are represented by three-dimensional and/or two-dimensional spectra and are compared with the available experimental data. The simulated dielectric spectra forecast that the sub-Tg relaxation should appear as a peak or shoulder of ε″ at lower-temperature and ultra-low-frequency regions in the ac measurements.

Sequential hydration-dehydration studies of lysozyme by the thermally stimulated depolarization currents (TSDC) technique

To investigate the physical state of water in hydrating biological macro-molecules, the dielectric properties of water in hen egg lysozyme pellets with various moisture contents were studied using the thermally stimulated depolarisation currents technique. The water dipoles appeared to be directly involved in the relaxation processes, such that, by increasing the content of water of sorption from ho = 0.075 to ho = 0.29, the current density recorded increased abruptly at moisture content above 0.075. At a fixed starting hydration level, the time evolution of water content was also studied by isothermal sample aging in dynamic vacuum: the TSDC spectra changed in both intensity and position of their main peaks (TM = 245 K, 190 K, 150 K) with moisture content and showed hysteresis. The complex behaviour of the TSDC response can be compared with the results obtained with the same technique on other biological macromolecules and suggests possible models for water configurations and rearrangements.

Thermally stimulated depolarization currents in poly(acrylamide) films

AbstractThe charge storage mechanism in poly(acrylamide) films was studied by means of the technique of thermally stimulated depolarization currents (TSDC). The TSDC were measured as a function of field strength, temperature and time of polarization in dependence on the heating rate. One peak was observed on the TSDC spectra at low polarizing temperatures, while two peaks occurred for higher polarizing temperatures. The first peak was attributed to dipole orientation and the second one to space charge polarization.

Dielectric effects of water in water-containing systems

The dielectric properties of several water-containing systems (synthetic polymers, saccharides, proteins, plant tissues) were systematically studied by means of the thermally stimulated depolarization currents (TSDC) method, following recently developed concepts for using the TSDC method to investigate the structures of water in different systems. The TSDC spectra recorded between 77 and 300 K exhibit several distinct relaxations which can be classified into three groups: relaxations due to the reorientation of water molecules themselves; dipolar relaxations, which are also present in the dry samples and which are influenced by water; and conductivity relaxations related with the water-dependent dc conductivity due to ions, mostly protons. In most cases, the results are compatible with a three-phase model: molecularly dispersed water tightly (non-rotationally) bound at primary hydration sites, loosely bound water in layers or clusters around primary hydration sites and free water at higher water contents.

Properties of urethane elastomers

The dielectric relaxation processes in poly(azourethaneurea) prepared from diphenylmethane-4,4′-diisocyanate (MDI) and poly(ethylene adipate) glycol were studied in the range 200–390 K using thermally stimulated depolarization currents (TSDC). The TSDC spectra obtained on original sample, annealed sample, and both annealed and stretched sample showed significant differences which were explained in terms of the supramolecular structure of polymers. It was accepted that the polymers have a multiphase supramolecular structure.

TSDC spectra in negatively corona charged ABS electrets

Corona charging technique has been used during polymer electret formation. Investigations of the thermally stimulated depolarization current (TSDC) in the electrets formed from Acrylonitrile-Butadiene-Styrene (ABS) terpolymer films were carried out. The optimum conditions for negatively corona-charged ABS films were determined. With the aid of partial heating technique, a single peak was obtained at T=381±2 K. This peak is associated with the temperature which was attributed to the motion of the bulk detrapping electrons arising from the thermal agitation as well as from erosion of the traps by the molecular motion. The activation energy of the process has been calculated. The electret property can be described in terms of dipolar relaxation process.

Energy parameters of defect dipole relaxation in Mg 2+ doped LiF

The energy parameters ( h m , τ 0) of cation motion in LiF single crystals doped with Mg 2+ were studied by two methods: (a) thermally stimulated depolarization currents (TSDC); and (b) depolarization currents ( T = constant) (DC). We demonstrate that the band of the TSDC spectrum is due to two kinds of dipoles; in contrast to other investigators who find only one. This probably explains the large scatter in the values of the cation migration enthalpy obtained by different investigators.

Electric relaxation study in poly( trans 1-octenylene) by the thermally stimulated discharge technique

The thermally stimulated depolarization currents (TSDC) spectrum of the poly( trans 1-octenylene) has been analysed by means of the thermal sampling technique over the 150–320 K temperature range. Three relaxation zones are defined. In the first zone, up to some degrees above T g ( ⋍208 K ) the relaxation is mainly dipolar, associated with motions in the amorphous phase, and the analysis reveals dipole-dipole interactions. In the second zone, above T g the relaxation takes place in the crystalline-amorphous interface. In the third zone, a relaxation at the crystalline phase is identified in the high temperature region. In addition, a shoulder localized in a narrow temperature interval (220–240 K) of the TSDC spectrum between the first and second zones is observed. It was found to be correlated with a change in the slope of the microhardness (Vickers) vs. T plot. This suggests a relation between the anomalous relaxation and the motion of the polymer chains bound to the crystalline-amorphous interface.

Thermally stimulated depolarization currents in PVDF-α: a dipolar interaction approach toβ andγ transitions

The analyst of the thermally stimulated depolarization current (TSDC) spectrum of theα phase of polyvinilide fluoride (PVDF-α) by means of the thermal sampling technique permits a series of elementary peaks to b8 obtained. The relaxation associated withγ andβ transitions is usually assumed to be due to dipolar motions; however, the relaxation time of these processes when represented as a function of the temperature does not follow an Arrhenius law. The definition of a relaxation time describing the experimental relaxation process requires, in addition to the frequency factor 1/τ0 and the activation energyE, a third parameter,q, which we call the interaction parameter. These considerations lead to defining a relaxation time, which accounts for the dipolar interaction during the relaxation. This relaxation time has successfully described thedipo!orrelaxation in other materials. The evolution ofq, obtained from the elementary peaks of the TSDC spectrum of PVDF-α, leads to the assignment of three relaxation zones, which are in agreement with those reported by other authors, as being associated with the molecular motion in the different phases of PVDF-α.

Etude de la relaxation dipolaire dans le Ce 2(S0 4) 3·9H 2O(9D 2O) monocristallin

We report in this article the resolution of TSDC (Thermally Stimulated Depolarization Current) spectra and the relaxation parameters of Ce 2(SO 4) 3· 9H 2O(9D 2O) single crystals, for two typical orientations parallel and perpendicular to C 6 , symmetry axes The TSDC peaks obtained show a nonDebye type of behavior Calculation of the dipolar relaxation parameters was achieved by fitting the experimental curves to a general order kinetic equation This method allows us to describe the nonDebye-type of behavior of the TSDC peaks on the basis of dipolar interactions during the relaxation process The three different kinds of electric dipoles leading to the three experimentally observed TSDC peaks are ascribed to three different configurations of hydrogen bonds.

Investigations on electric properties of polymers—II. Dielectric relaxation in atactic polystyrene determined by thermally stimulated depolarization currents

The thermally stimulated depolarization currents (TSDC) from atactic polystyrene and d.c. conductivity of the same material have been studied over the temperature ranges 200–395 K and 363–393 K respectively. TSDC spectra are complex and consist of four peaks, β 1, β 2, β 3 (β 3 of reduced intensity) and α in order of increasing temperature. The first three peaks appeared below the glass transition temperature T g of the polymer. The β 1 peak seems to arise from a single dipolar relaxation process. The β 2 peak and probably β 3 arise from a distribution in activation energy of dipolar relaxation processes. On the basis of the molecular origin of the β relaxation process, it was suggested that β 1, β 2 and β 3 peaks involve motions of backbone chain fragments of various lengths. The last peak α appeared at T g and could be considered as a result of dipole relaxation and electric conductivity. TSDC peaks and d.c. conductivity have been related to the second order transition in the polymer.