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Plaques of blends of Eudragit RL 100 (EU) and poly(methyl methacrylate) (PMMA) with different weight-per-weight ratios were prepared by compression molding at 150°C. The X-ray diffraction profiles of the blends were studied and compared, and the interplanar distance, crystallite size, and crystallinity were computed for various peaks. The Eu/PMMA blend with a 70:30 (w/w) ratio had the maximum crystallinity.

Specimens of poly(vinyl formal) (PVF) : poly(methyl methacrylate) (PMMA) polyblends with different weight percentage ratios were subjected to gamma irradiation (1 to 50 Mrad) and electron irradiation (1 to 20 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vickers microhardness number, Hv. The Hv values of gamma irradiated specimens are found to be higher than the unirradiated specimens indicating an occurrence of radiational crosslinking. The maximum value of Hv is obtained at the gamma radiation dose of 15 Mrad. In case of electron irradiation the radiational crosslinking is found to take place for the blend specimens having lower wt% content of PMMA (0 and 1 wt%) in PVF matrix. On the other hand degradation of polymeric system is observed for the blends having PMMA content more than 1 wt‰ The maximum value of Hv is obtained for all the blend specimens at the electron irradiation dose of 8 Mrad. The degree of crosslinking in polyblends due to gamma irradiation is found to be more than electron irradiation. The scissioning mechanism is found to predominate in the polyblend system in case of electron irradiation.

Plaques of blends of Eurdragit RL 100 and poly(methyl methacrylate) (PMMA) with different weight percentage ratios were obtained by compression moulding at 150°C. The mechanical strength of these blends was studied by a microindentation technique. The results show a decrease in brittleness and increase in hardness, toughness and yield strength by addition of PMMA to Eudragit.

Mechanisms of charge generation and its persistence in one and both-side vacuum-aluminized ethyl cellulose (EC):polymethyl methacrylate (PMMA) blend thermoelectrets, prepared under different fields (10, 25, 50 and 100 kV/cm) and temperatures (40, 60, 80 and 100°C), have been analysed using short- and open-circuit thermally stimulated depolarization current (TSDC) technique. The TSDCs were recorded by reheating the samples at a linear heating rate of 4°C/min. The TSDC thermograms of polyblends containing EC:PMMA in different weight ratio are, in general, characterized with two peaks in lower and higher temperature regions. However, the polarity of the peaks was found to be just opposite in short- and open-circuit TSDC measurements. Moreover, results on 97:3, 93:7 and 90:10 EC:PMMA polyblends indicated that the current increases with concentration of PMMA. The results indicate the existence of heterocharge due to dipole orientation and ionic charge drift together with the injection of charge carriers from electrodes with their subsequent localization in surface and bulk traps. Further, the chances of charge trapping in polyblends, at the interfaces are greater than in the individual polymers.

Thermally stimulated currents (TSCs) in short-circuit and open-circuit configuration for ethyl cellulose samples (≈40 µm thick) have been studied as a function of polarizing field (25–100kV/cm) and polarizing temperature (323–353K). The thermograms have been found to be characterized by two prominent peaks located around 70 ± 10°C and 140 ± 10°C and the appearance of anomalous current in the high temperature region of the short-circuit TSC thermograms. The observed behaviour has been explained in terms of the existence of heterocharge due to dipole orientation and ionic homocharge drift, together with the injection of charge carriers from electrodes and their subsequent localization in surface and bulk traps.

Specimens of poly(methyl methacrylate) (PMMA) and poly(chloro trifluoroethylene) (PCTFE) polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1–100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using the Vicker's microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. The value of Vicker's hardness number, H v , was found to increase up to 5 wt% of PCTFE, beyond which decrease in hardness level was observed. Thus the maximum value of H v was observed in the blends having 5 wt% of PCTFE. Also, a general increase in the microhardness level was observed in the irradiated specimens as compared to the untreated blends. The blends became brittle after the irradiation dose of 100 Mrad and indentation testing resulted in the cracking of the specimens.

The dark conduction current in 100 μm thick pure and anthracene doped bimetallized poly(methyl methacrylate) (PMMA) foils was measured at temperatures ranging from 333 to 383 K and filds ranging from 8 to 50 kV/cm. An attempt was made to identify the nature of the current by comparing its observed dependence on electric field, temperature and dopant concentration with the respective characteristic features of the existing theories of electrical conduction. The observed characteristics suggest that the charge carriers are generated by field assisted lowering of coulombic barriers at the traps and are conducted through the bulk of the material by a hopping process between the localized states by a Jonscher–Ansari modified Poole–Frenkel mechanism. The high value of the activation energy is considered to indicate the possibility of charge carrier species inside the polymer bulk being ionic in nature.

The electrical conductivity of solution-grown ethyl cellulose (EC) films, 5–30 μm thick, has been studied in the sandwich configuration (metal–EC–metal) as a function of iodine concentration from 0.5 to 5.0 wt% ratio. The studies were conducted in the temperature range 333–383 K, while the field was varied over the range (3.0–5.5) × 104V/cm. Aluminium was used as the lower electrode, while the upper electrode was of Al, Ag, Cu, Au or Sn. Certain transient effects such as a large burst of current immediately after the application of field were observed. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories of electrical conduction. The results show that the electrical conduction follows Ohm's law at lower fields, while at higher fields, space-charge limited current (SCLC) was observed. It was also found that Richardson–Schottky emission was responsible, to some extent, for the transport of charge carriers in the polymer. The conductivity of the films increased on doping with iodine. The dopant molecules are considered to act as additional trapping centes and provide links between the polymer molecules in the amorphous region, thus resulting in the formation of charge transfer complexes.

The method of preparation of polymer blends of poly (methyl methacrylate) and poly (chlorotrifluoroethylene) with different ratios of the two polymers is described. The effect of load and ratio of the two polymers in the polyblend on the Vicker's microhardness has been studied. It is observed that poly (chloro trifluoroethylene) acts as a plasticizer for poly (methyl methacrylate).

The effect of annealing and quenching temperatures on the morphology of glass-fibre reinforced polymer (GFRP) has been studied utilizing the Vickers microhardness H v tests as an analytical tool. Increase in annealing temperature results in two peak values of H v at 60 and 180°C. The quenching temperature in different mediums, viz. air, water and ice-water, first increases H v up to 60°C, and then decreases it up to 140°C. Thereafter, H v goes on increasing ut to its melting point of 260°C. The value of H v of ice-water quenched specimens is higher than those of air and water quenched specimens. The quenching behaviour has been explained on the basis of an empirical relationship between quenching temperature and microhardness.

Specimens of PS:PMMA polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1 to 75 Mrad) and electron irradiation (1 to 30 Mrad). The effect of these irradiations on the strength of blend specimens has been studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU-2 Universal research microscope. The irradiation was found to produce crosslinking behaviour in the specimens and the crosslinking degree is related to the type and dose of irradiation and to the miscibility of PS and PMMA in the blend.

Solution-mixed poly(methyl methacrylate) (PMMA): poly(vinylidene fluoride) (PVDF) polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1–100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU-2 Universal research microscope. The irradiation was found to produce hardening in the blend specimens; however, the degree of hardening depends upon the dose level, testing conditions and also on the miscibility of PMMA and PVDF in the blend specimens. The increase and decrease in microhardness has been explained on the basis of crosslinking and scissioning. The two limits of irradiation dose were 1 and 75 Mrad where significant changes in mechanical strength were observed.

The influence of chemical environment on polymers include the surface alteration as well as other deep modifications in surface layers. The surface hardening, as an effect of organic liquids on poly(methyl methacrylate): poly(vinylidene fluoride) (PMMA: PVDF), which is one of the few known miscible blends, has been detected using microhardness testing. Organic liquids like acetone, toluene, xylene and benzene were introduced on the surface of blend specimens for different durations. Vickers microhardness (H v) was measured for treated and untreated specimens. The study reveals both hardening and plasticization of specimens at different exposure times. The degree of surface hardening is maximum under acetone treatment. All the specimens exhibit surface hardening at an exposure time of 1 h with all the four liquids. This feature is prominent with longer exposures for specimens with increasing content of PVDF. However, the degree of hardening decreases with the time of exposure in the respective environments. In general, acetone and toluene impart surface hardening, whereas, xylene and benzene soften the specimen. PMMA: PVDF (83 : 17) blend exhibits surface hardening under all the four treatments when compared with the respective untreated specimens.

The dark current in commercial polypropylene (PP) is measured at temperatures ranging from 333 to 413 K and fields ranging from 70 to 125 kV/cm. The specimens are metallized on both sides by evaporated layers of silver and aluminium. An attempt is made to identify the nature of the current by comparing its observed dependence on electric fields, electrode material, and temperature with the respective characteristic features of the existing theories of electrical conduction. The observed results suggest that the electrical conduction in PP is governed by a Jonscher-Ansari modified Poole-Frenkel mechanism.

The Vickers microhardness test is found to be a suitable analytical method for studying thermal change in thin films of polymers. It is utilised to analyse the effect of thermal pretreatment (annealing and quenching) on the surface microhardness of guargum (GG); a natural polymer), polyacrylonitrile (PAN; a synthetic polymer) and their cast blends, guargum-grafted-polyacrylonitrile (GG-g-PAN) and polyacrylonitrile-guargum (PAN-GG). Annealing at various temperatures reveals the change in configuration and crystallinity of thin films of polymers. Peak values of hardness are found to occur in GG, PAN and PAN-GG but not in GG-g-PAN. The quenched hardness for GG is found to be nonlinear with temperature. However, for other polymers quenched hardness decreases, initially, up to a certain temperature and then starts increasing; such temperatures for PAN, PAN-GG and GG-g-PAN are 86, 66 and 86°C, respectively. The behaviour of polymer blends on quenching can be represented by a calculated value of the exponent which is 0·62 and 0·75 for GG-g-PAN and PAN-GG, respectively.

The application of the network formed from ethylene glycol dimethacrylate and poly (methyl methacrylate) (PMMA) in dentistry and orthopaedics has generated interest among material scientists in the study of its mechanical behaviour. This paper reports the preparation of the network polymer with varying concentrations of PMMA in the network and its effect on the Vickers microhardness (Hv) of the specimens at different loads ranging from 80 to 160 g. The increasing and decreasing trend in values of Hv have been observed with varying concentrations of PMMA in the network. The observed behaviour has been attributed to the effect of localized plastic deformation and cross-linking density. The role of phase separation has also been envisaged.

Thin films of polystyrene-ferrocene (PSFe) composite were irradiated with various doses of gamma irradiation ranging from 4·1 to 25·3 Mrad. The Vickers hardness number (Hv) was calculated for pure and irradiated specimens. It was used to analyse mechanical strength at a saturation load of 100 g. The mechanical strength was found to increase with irradiation dose up to 12 Mrad. Brittleness of the composite PS-Fe was found to occur at a higher dose of 25 Mrad as compared to 15 Mrad for polystyrene. Further, fracture toughness, brittleness index and yield strength were calculated for various irradiated specimens consequent to crack propagation in the specimens.

Thin films of guar gum (GG)—a natural polymer, polyacrylonitrile (PAN)—a synthetic polymer, GG grafted with PAN, and a composite of GG and PAN were made by the usual solvent evaporation method. All the four films were subjected to Vickers microhardness tests in order to explain surface morphology, crystallinity and composition. The breaking strength of all the films was also determined. The load dependence of Vickers microhardness, Hv, has been explained by a logarithmic index, n. The small stress behaviour of Hv was found to be related to the Newtonian resistance pressure of the specimen itself.

The Vickers microhardness test has been carried out on GFRP specimens at different loads ranging from 5 to 160 g. The Vickers hardness number (H v )-load behaviour has been explained on the basis of strain hardening phenomena. This reveals that the value of H v is greater at small stresses and it becomes independent of load beyond 110 g. In this range the value of the logarithmic index, n, is 2. The non-linear behaviour of microhardness with load has three different values of logarithmic index. Further, the dependence of load on H v in GFRP specimens has been explained on the basis of Newtonian resistance pressure as proposed by Hays and Kendall.

GFRP specimens were irradiated with various doses of gamma and electron radiations ranging from 60 to 200 Mrad. Tensile tests using an Instron Model-1185 have been utilized to study the effect of these radiations on the mechanical strength of GFRP. A typical load-elongation curve of this composite consists of two stages. The first stage is linear, and the deformation produced is elastic. Beyond the first linear stage, the change of slope of the curve is attributed to the initiation and extension of cracks at fibre ends. Evidence of decrease as well as increase in the strength of specimens has been observed at different doses of radiation. The electron irradiation increases the strength of GFRP at all doses of irradiation except 200 Mrad. However, gamma irradiation decrease the strength of GFRP. The ductile and brittle character of GFRP has been explained.

The preparation of polymer blends of poly(methyl methacrylate) and poly(vinylidene fluoride) in different weight percentages is described. Vickers microhardness measurements have been made to study the effects of load and compositional ratio of the two polymers in polyblend. It is observed that poly(vinylidene fluoride) acts as a plasticizer for poly(methyl methacrylate). Evidence of increasing and decreasing strength of polyblends has been obtained for different compositional ratios of the two polymers.

Vickers microhardness testing has been utilized to study plasticization effects in environmentally-affected commercial polypropylene. The paper provides experimental evidence on the effect of some organic liquids and acids on the surface microhardness of polypropylene at different loads and different pouring times of liquids.

GFRP specimens were irradiated with various doses of gamma irradiation ranging from 40 to 250 MRad. The Vickers microhardness test has been utilized to study the effect of irradiation on the mechanical behaviour of GFRP at different loads. Evidence of both the decrease and increase in the strength of specimens has been observed at different doses of irradiation.

The preparation of polymer blends of polystyrene and poly(methyl methacrylate) in different weight percentages is described. The strengths of these blends have been studied by measuring their surface microhardness making use of a Vickers microhardness tester.

The absorption currents in the discharge mode of acrylic-acid (AA)-doped solution-grown polystyrene (PS) films, prepolarized at 358 K with different fields, have been analyzed in the temperature range 313-358 K. Space charge due to trapping of injected charge carriers in energetically distributed traps is considered to account for the observed currents. Two relaxation peaks centered at 328 K and approximately at 348 K, respectively have been observed in isochronal current thermograms. >

The short-circuit thermally stimulated discharge (TSD) currents for isotactic commercial grade polypropylene (PP) foil thermoelectrets, poled under different field and temperature conditions, indicate the distribution of traps in energy. Anomalous TSDCs flowing in the same direction as the charging current, observed in electrets poled above 100 degrees C, are attributed to injected space charges and the blocking condition of the electrodes. Experimental data indicate that as the carrier mobility increases with the temperature and as the density of injected space charge increases with the applied field, a high charging field and a high temperature result in a high rate of return of carriers to the injecting electrode. >

Details are reported of short- and open-circuit thermally stimulated current (TSC), isothermal charge decay, and absorption current measurements. These measurements were conducted on corona-charged 50- mu m-thick commercial-grade isotactic polypropylene (PP). The appearance of a peak centered at 140 degrees C in open-circuit TSCs that is absent in short-circuit TSCs shows that this peak is due to the charge trapped in trapping sites located at the surface or in the near-surface region. However, the traps giving rise to three other peaks common to both type of TSCs are clearly bulk traps. Anomalous short-circuit TSCs (flowing in the same direction as the charging current), observed for high-temperature-charged samples, can be understood in terms of space-charge-limited drift of charge carriers toward the collecting electrode. >

The electrical conductivity of acrylic-acid (AA)-doped polystyrene films (about 100- mu m thick) has been studied as a function of temperature in the range 20-85 degrees C. Power-law dependence of current on voltage has been observed at various temperatures. The value of the power has been found to decrease with increasing temperature and also with increasing dopant concentration. The conductivity was found to increase with an increase in dopant concentration. These effects have been attributed to the formation of charge-transfer complexes (CTCs). >

Thermally stimulated currents (TSCs) from iodine-doped polystyrene (PS) thermoelectrets have indicated that the polarization is due to the localization of an injected charge in geometrically and energetically distributed traps. Anomalous TSCs, observed with strongly doped samples, are considered to be due to the release of injected space-charge carriers and the partial blocking of the metal-polymer contact. As the number of shallow traps with small detrapping increases with increasing dopant concentration, the space-charge density will be relatively greater in room-temperature-charged samples with strong doping than in samples charged at this temperature with weaker doping. >

Investigations of short-circuit thermally stimulated depolarization currents have been made on 20- mu m-thick, polystyrene-polymethyl-methacrylate (PS/PMMA) blends containing different weight percentages of PMMA. The observed currents decrease for higher values of the forming field and temperature and eventually become anomalous. These characteristics are considered to be due to the screening effect of the space charge formed near the electrodes. The TSDC (thermally stimulated depolarization current) characteristic have been found to be sensitive to blend composition. >

Specimens of poly(methyl methacrylate) (PMMA): poly(chlorotrifluoroethylene) (PCTFE) polyblends with different weight percentage ratios were subjected to electron beam irradiation (1–10 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vicker's microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vicker's hardness number, Hv. An irradiation dose of 3 Mrad was found to enhance greatly the microhardness level of the specimens. An increase of approximately 78% in microhardness was observed as the radiation dose was increased from 1 to 3 Mrad. Electron irradiation was also found to induce crosslinking and degradation in the material. The degree of crosslinking was found to be maximum at a dose of 3 Mrad. Specimens incorporating 10 wt% PCTFE were found to exhibit the highest level of microhardness at all radiation doses.

The charge storage and transport behaviour of 100 /spl mu/m thick pure and 0.1 wt% anthracene doped poly(methyl methacrylate) (PMMA) foils has been investigated by absorption current, isothermal surface charge decay and thermally stimulated discharge current (TSDC) measurement techniques over a temperature range of 298 to 393 K, with fields ranging from 8 to 50 kV/cm.

Thermally stimulated depolarization current (TSDC) characteristics in short circuit have been studied in laboratory grown 100 /spl mu/m PVC and PVC:PMMA blend films of different wt.% composition ratio thermally polarized with fields of 25, 50, 60 and 75 kV/cm at temperatures 50, 70, 90 and 110/spl deg/C. The TSDC thermograms exhibit a broad hump between 50 to 90/spl deg/C and a well defined peak between 128 to 148/spl deg/C. The high peak is considered to be associated with polarization due to space charge accumulated at the crystalline amorphous boundaries. The hump observed between 50-90/spl deg/C is attributed to the relaxation of dipoles connected to the main chain of PVC having a continuous spectrum of activation energies and relaxation times.

The dielectric ac bridge measurements have been carried out to understand molecular motion and their relaxation behaviour in PMMA:PVDF polyblends of different wt% composition. The dielectric constant (/spl epsiv/') and dielectric loss (/spl epsiv/") factors of 100 /spl mu/m thick films of these polyblends were measured as a function of temperature in the range of 40 to 140/spl deg/C and at different frequencies from 100 Hz to 10 MHz. The dielectric constant decreased with frequency and increased with temperature in the entire frequency range. The dielectric loss also increased with temperature in the studied frequency range. The observed characteristic behaviour has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending PMMA with PVDF.

The electrical transport behaviour of ferrocene mixed polymethylmethacrylate (PMMA) films (approximately 20 microns in thickness) deposited by the isothermal immersion technique has been studied in the temperature range of 333-373 K and field from (2.0-4.0)/spl times/10/sup 4/ volts/cm. It has been found that at higher fields and temperatures, the observed conduction behaviour could be consistently described by the Richardson-Schottky emission. Increase in current due to doping has been attributed the formation of charge transfer complexes. The dopant molecules acts as an additional trapping centre and provide a link between polymer molecules in the amorphous region leading to the formation of a charge transfer complex.

The charge storage and transport behaviour of bimetallized, 100 /spl mu/m thick, pure and anthracene doped poly methyl methacrylate (PMMA) foils has been studied by investigating dark conduction currents, transient absorption currents and thermally stimulated depolarization (TSD) over a wide temperature range of 298 to 393 K, with fields ranging from 8 to 50 kV/cm.

Transient currents were measured in discharge mode with ethyl-cellulose (EC):polymethyl methacrylate (PMMA) compound samples as a function of charging field, temperature, and polymer weight ratio. These currents have been found to follow the Curie-von Schweidler law characterized with different slopes in short and long time regions. The isochronals have been found to give rise to a peak located at 80 degrees C. The corresponding activation energy values are found to increase with PMMA content and also with time of observation of discharge current. >

Thermally stimulated currents (TSCs) in short- and open-circuit configuration for thermally poled ethyl cellulose (EC) foil samples have been found to be characterized with two prominent peaks located around 70 and 100 degrees C. Various characteristics of these thermograms along with currents of opposite polarity in short- and open-circuit, and the appearance of anomalous current in the low temperature region of short-circuit TSC thermograms have been considered to be indicative of intense charge trapping in surface and bulk traps and of the injection of carriers from electrodes under strong field at the near-surface region created by heterocharges. >

Mechanisms of charge production and its persistence in one and both side vacuum-aluminized EC:PMMA blend foil thermoelectrets, prepared under different field and temperature conditions, have been analyzed using the short- and open-circuit thermally stimulated current (TSC) techniques. The results indicate the existence of heterocharge due to dipole orientation and ionic charge drift together with the injection of charge carriers from electrodes with their subsequent localization in surface and bulk traps. Various characteristics of both types of thermograms indicated the injection of charge carriers from electrodes during short-circuit TSC under high electric field created at the interface by the strong heterocharge. >

Short-circuit thermally stimulated current (TSC) measurements have been made on thermally polarized foils. The results indicated that the electret state of these samples is due to dipolar orientation and charge trapping. Iodine doping has been found to form a charge transfer complex and hence to modify the electret state of the samples significantly. Higher concentration of doping and charging at higher temperatures has been found to favor charge carrier trapping in energetically deeper traps. An anomalous peak observed in strongly doped samples polarized at higher temperatures is considered to be due to detrapping of carriers from such deeper traps. >

A total of 34 pea (Pisum sativum L.) genotypes including 7 adapted varieties, 6 popular local cultivars and 21 advanced breeding lines developed through crossing of elite cultivars were evaluated for genetic diversity and relatedness with 16 morphological traits and 15 SSR markers. Genotypes viz., DDR-23, E-6, Makuchabi and KPMR-885 were identified as early flowering while Rachna, IPFD 09-2, CAU FP-1, IPFD 1–10 and Pant P-136 were identified as high yielding. The number of alleles per SSR marker varied from 2 to 5 per locus. Polymorphic information content values (PIC) ranged from 0.105 to 0.560 per locus. Variability among groups (FIS=0.938) and variability within individuals (FIT=0.948) was low. The minimum and maximum molecular genetic distances were found to be 0.12 (Pant P-136 with VL-51) and 0.78 (E-6 with LP-4) respectively. Genotypes IPFD 09-2, HFP-620, Azad P-1, Matek, IPFD 1–10, CAU FP-1, IPFD 09-3, Pant P-136, Rachna, E-6, Matek and LP-3 showed high level of genetic diversity. Pea improvement through hybridization by utilizing diverse genotypes is suggested for breeding suitable genotypes for North Eastern region.

Absorption currents observed at various temperatures in charging mode with ethyl cellulose (EC) foil samples, prepoled under different field conditions, have been found to follow the I varies as t/sup -n/ (i.e., Curie-von Schweidler law) time dependence with different values of n at short and long times. The isochronals have been observed to be characterized with a peak located at 60 degrees C. Activation energy values for this peak are observed to vary from 0.5 to 2.4 eV. In some cases the observed current tends to increase with time in the longer-time region, indicating the possibility of the existence of a peak at still longer times, similar to that found in space-charge-limited transients. >

A detailed study of current as a function of voltage coupled with that of the thermoelectret state has been undertaken in sisal wax. Below 65°C, Ohm's law is seen to be followed at low voltages, while at higher voltages space-charge-limited conduction following a power-law dependence of current on voltage has been observed. A complete study of the current as a function of voltage, temperature, and thickness indicates an exponential distribution of trapping states in the band gap which is found to be about 7.38-eV wide. Voltage dependence of the quasi-Fermi energy, Ef, has been shown to be consistent with the filling of an exponential trap distribution. The dependence of the initial charge densities on the polarizing field and temperature, and their decay with time have shown that the electret state is due to the localization, in different trapping states, of charges which have a double origin: the injection from the electrodes and a thermally activated production of electron—hole pairs in the bulk. The observed initial positive charge densities on one-sided metallized sisal wax samples correspond to trap densities of the order of 1012 cm−3.

A careful study was undertaken of the initial charge developed on the non-metallized surface and of short-circuit thermally stimulated currents (TSCs) in unilaterally metallized polystyrene (PS) films 25 microm thick. The films had been negatively charged by Townsend breakdown at a voltage of −5 kV at various temperatures ranging from 90 to 130°C. The surface charge densities observed were of the order of 10-8 C cm-2, corresponding to full trap densities of the order of 1014 cm−3. The short-circuit TSC spectra of newly charged samples show a single peak at a temperature between 98 and 102°C. The thermal activation energy associated with this peak was found to be 1.2 eV. An analysis of TSCs indicates that electrons are subject to fast retrapping in PS. The ratio of the mean charge depth to the sample thickness is found to increase from 0.069 to 0.12 with the increase in the temperature of polarization, indicating a higher charge accommodation at higher temperatures of polarization. The trap-modulated mobility values for electrons at the TSC peak temperatures are the order of 10−12 cm2 V−1s−1. Such low mobility values at peak temperatures are considered to indicate the excellent charge storage properties of PS.

Irradiation gamma a des doses entre 2 et 75 Mrad; calcul du nombre de durete de Vickers Hv. Diminution de Hv en augmentant la dose jusqu'a 50 Mrad, puis accroissement brusque. Interpretation par des ruptures de chaine et la reticulation du polymere

Etude de l'effet de la charge sur le nombre de Vickers. Discussion de la nature des polymeres selon la loi de Meyer et en fonction de leur comportement aux contraintes faibles a l'aide de la pression de resistance newtonnienne

A detailed study of the initial charge developed on the nonmetallized surface, coupled with that of short-circuit thermally stimulated currents (TSC), has been undertaken in breakdown-charged one-sided metallized 25 μm polystyrene foils. The observed surface charge densities are of the order of 10 −8 C cm −2 . Short-circuit TSC spectra of freshly prepared electrets show a dominant high-temperature peak and two other peaks of small magnitude at lower temperature. The polymer does not become totally discharged before reaching its softening point at 125°C. Analysis of thermally stimulated currents indicates that the electrons are subject to fast retrapping in this polymer. The largest ratios of the mean charge depth to the sample thickness, obtained for electrets depolarized soon after charging and 24 h after changing, are found to be 0.08 and 0.17, respectively. This increase is considered to be due to electron retrapping at various energy levels. The observed initial released charge densities correspond to full-trap densities of the order of 10 15 cm −3 .

Mesure des courants thermostimules en circuit court et ouvert, de la diminution de charge isotherme et des courants d'absorption d'electrets de polypropene

A study of thermally stimulated charge-decay (TSCD) in conjunction with that of short-circuit thermally stimulated current (TSC) is undertaken in unilaterally metallized 26 μm thick polypropylene (PP) films. The films are negatively corona charged with various corona voltages varying from 7 to 9 kV at temperatures of 313 K and above and the charge stability of such samples is investigated using the above two techniques. The TSCDs and TSCs indicate a considerable increase in the stability of charge in the samples charged above 353 K which is considered to be due to the localization of charge carriers in deep traps at higher charging temperatures. The present study thus confirms that stable electrets suitable for practical use can be obtained by corona charging at higher temperatures. Das Abklingen des thermisch stimulierten Stromes (TSCD) wird in Verbindung mit dem thermisch stimulierten Kurzschlusstrom (TSC) in einseitig metallisierten 26 μm dickcn Polypropylenschichten (PP) untersucht. Die Schichten werden negativ koronageladen mit unterschiedlichen Koronuspannungen zwischen 7 und 9 kV bei Temperaturen von 313 K und daruber, wobei mit den genannten Methoden die Ladungsstabilitat derartiger Proben untersucht wird. Die Ergebnisse der TSCD und TSC zeigen einen betrachtlichen Anstieg der Ladungsstabilitat in den oberhalb 353 K geladenen Proben, und es wird angenommen, das er durch die Lokalisierung von Ladungstragern in tiefen Haftstellen bei hoheren Temperaturen verursacht wird. Die Untersuchung bestatigt somit, das stabile Elektrete, die fur den praktischen Gebrauch geeignet sind, durch Koronaauf ladung bei hoheren Temperaturen erhalten werden konnen.