Infrared studies of drawn polyethylene part I. Changes in orientation and conformation of highly drawn linear polyethylene

Infrared spectroscopy is applied to discuss the orientation, the crystallinity, and the conformation of chain segments in the amorphous regions in drawn high-density polyethylene. The orientation of the crystals as well as the crystallinity are derived from the dichroism and the absorbance, respectively, of the band at 1894 cm-¹. The orientation and some aspects about the conformation of the chain segments in the amorphous regions can be obtained from the bands in the 1400-1300 cm-¹ region (gauche) and at 1078 cm-1 (gauche and trans). The dichroic studies show a high degree of orientation increasing with draw ratio λ for the chain segments in the crystals, but a low orientation reaching saturation at λ between 5 and 10 for those in the amorphous regions. The experiments indicate a change in crystallinity during the drawing process which depends on the thermal treatment of the undrawn sample. In the amorphous regions the number of CH₂ groups in gauche conformations decreases up to λ between 10 and 15 and remains nearly constant with further drawing. Since the sum of gauche and trans conformations remains unchanged, it can be deduced that the number of loops decreases and that of tie molecules increases with draw ratio.     

Effect of electron irradiation on InSb microcrystals

The results of experimental studies of electrophysical properties of heavily doped n-InSb whiskers exposed to electron irradiation (13 MeV, 300 K) are reported. The limiting electrophysical parameters and the problem of the Fermi-level pinning in irradiated InSb are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 42–45, February, 2006.     

Effect of gamma irradiation on high temperature hardness of low-density polyethylene

Gamma irradiation can cause the change of microstructure and molecular structure of polymer, resulting in the change of mechanical properties of polymers. Using the hardness measurement, the effect of gamma irradiation on the high temperature hardness of low-density polyethylene (LDPE) was investigated. The gamma irradiation caused the increase in the melting point, the enthalpy of fusion, and the portion of crystallinity of LDPE. The Vickers hardness of the irradiated LDPE increases with increasing the irradiation dose, annealing temperature, and annealing time. The activation energy for the rate process controlling the reaction between defects linearly decreases with the irradiation dose. The process controlling the hardness evolution in LDPE is endothermic because LDPE is semi-crystalline.     

Impact of silver metallization and electron irradiation on the mechanical deformation of polyimide films

The impact of silver metallization and electron irradiation on the physical and mechanical properties of polyimide films has been studied. The metal that impregnated the structure of the polyimide substrate was 1–5 μm. The surface coatings contained 80–97% of the relative silver mirror in the visible and infrared regions. Irradiation was performed at the ELU-6 linear accelerator with an average beam electron energy of 2 MeV, an integral current of up to 1000 μA, a pulse repetition rate of 200 Hz, and a pulse duration of 5 μs. The absorbed dose in the samples was 10, 20, 30, and 40 MGy. The samples were deformed at room temperature under uniaxial tension on an Instron 5982 universal testing system. The structural changes in the composite materials that result from the impact of the physical factors were studied using an X-ray diffractometer DRON-2M in air at 293 K using CuK_α radiation (λ_αCu = 1.5418 Å). A substantial growth of mechanical characteristics resulting from the film metallization, as compared to the pure film, was observed. The growth of the ultimate strength by Δσ = 105 MPa and the plasticity by Δε = 75% is connected with the characteristics of the change of structure of the metallized films and the chemical etching conditions. The electron irradiation of the metallized polyimide film worsens its elastic and strength characteristics due to the formation of new phases in the form of silver oxide in the coating. The concentration of these phases increased with increasing dose, which was also the result of the violation of the ordered material structure, namely, the rupture of polyimide macromolecule bonds and the formation of new phases of silver in the coating. A mathematical model was obtained that predicts the elastic properties of silver metallized polyimide films. This model agrees with the experimental data.     

Effect of electron irradiation on the oxidation of indium

The oxidation kinetics of indium is studied for two cases, namely, during continuous electron irradiation (E _p = 1800 eV) and without electron irradiation, as a function of the time of exposure to an oxygen medium at a partial oxygen pressure of 10⁻⁴ Pa and room temperature. The initial oxygen exposure was 50 L. The kinetic curves recorded upon continuous electron irradiation have two inflection points, and they can be attributed to the following three states of oxidation: physical adsorption, chemisorption with the formation of a nonstoichiometric oxide layer, and the growth of a homogeneous oxide layer. Only the first inflection point is observed during oxidation without electron irradiation, and further exposure does not lead to the second inflection point within the experimental time.     

Effect of high-energy electron irradiation on forsterite laser crystals

The effect of 21-MeV electron irradiation on the optical absorption characteristics of Czochralski-grown forsterite (Mg₂SiO₄) single crystals (both undoped and chromium-doped) has been investigated. The irradiation is found to induce additional optical absorption (AOA) in the crystals in the range of 225–1200 nm due to the formation of color centers based on intrinsic host point defects and the change in the oxidation state of chromium ions. The AOA spectra have been decomposed into elementary bands. The influence of the chromium concentration in crystals, the oxygen content in the growth atmosphere, and additional doping with lithium on the behavior of these bands has been analyzed. A possible structure of the color centers responsible for the AOA is discussed. It is shown that the electron irradiation somewhat decreases the intensity of the characteristic absorption bands of tri- and tetravalent chromium ions and gives rise to a new absorption band in Mg₂SiO₄:Cr and Mg₂SiO₄:Cr,Li crystals heavily doped with chromium.     

Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation

Surface free energy of biocompatible polymers is important factor which affects the surface properties such as wetting, adhesion and biocompatibility. In the present work, the change in the surface free energy of ultra-high molecular weight polyethylene (UHMWPE) samples, which is produced by electron beam and gamma ray irradiation were, investigated. Mechanism of the changes in surface free energy induced by irradiations of doses ranging from 25 to 500 kGy was studied. FTIR technique was applied for sample analysis. Contact angle measurements showed that wettability and surface free energy of samples have increased with increasing the irradiation dose, where the values of droplet contact angle of the samples decrease gradually with increasing the radiation dose. The increase in the wettability and surface free energy of the irradiated samples are attributed to formation of hydrophilic groups on the polymer surface by the oxidation, which apparently occurs by exposure of irradiated samples to the air.     

Effect of electron irradiation on creep and dislocation structure of aluminium

The effect of electron irradiation and strain on structure of technical-purity aluminium subjected to constant-load tensile creep tests was investigated. The dislocation structure was statistically analyzed. The effect of electron irradiation appears in the creep rate reduction and generation of radiation defect clusters, the density of which is approximately proportional to the dose. The effect on the dislocation distribution is dependent on the dose as well. Doses1·2×10¹⁷ cm^–2 speed up the formation of a polygonal structure characterizing the steady-state creep.     

Effect of crosslinking on the low-temperature relaxation behavior of polyethylene

The dynamic mechanical properties of polyethylene crosslinked by chemical methods and by electron irradiation were determined from 77°K to 250°K on an acoustic spectrometer at a frequency of approximately 50 Hz. Parallel stress-strain, swelling, and x-ray scattering experiments were also carried out to determine the degree of crosslinking and crystallinity. It is found that the effect of chemical crosslinking is to suppress the loss intensity of the γ relaxation in polyethylene while preserving the symmetrical shape of the loss curve without changing the temperature position. The effect of radiation crosslinking, however, also changes the symmetrical nature of the curves. Possible mechanisms of these observed changes are discussed.     

The impact behavior of polyethylene: A new vista

Recent advances in the analysis of the fracture behavior of polyethylene have been reviewed specifically to establish the nature and extent of morphological changes. It has been shown that in the case of linear low-density polyethylene (LLDPE), reorganization and orientation of lamellae occur in the shear lips region, the pattern being influenced by differences in molecular structure. Crazes, on the other hand, are characterized by the presence of voiding, with no significant effect on the original morphology.     

Effect of high temperature electron irradiation in gold

Pure gold is electron irradiated with 2.8 MeV electrons at 450±50°C. Both electrical resistivity and transmission electron microscopy showed damage which anneals at about 800°C.     

Effect of MeV electron irradiation on the free volume of polyimide

The free volume of the microvoids in the polyimide samples, irradiated with 6 MeV electrons, was measured by the positron annihilation technique. The free volume initially decreased the virgin value from ～13.70 to ～10.98 Å³ and then increased to ～18.11 Å³ with increasing the electron fluence, over the range of 5?×?10¹⁴ – 5?×?10¹⁵ e/cm². The evolution of gaseous species from the polyimide during electron irradiation was confirmed by the residual gas analysis technique. The polyimide samples irradiated with 6 MeV electrons in AgNO₃ solution were studied with the Rutherford back scattering technique. The diffusion of silver in these polyimide samples was observed for fluences >2?×?10¹⁵ e/cm², at which microvoids of size ≥3 Å are produced. Silver atoms did not diffuse in the polyimide samples, which were first irradiated with electrons and then immersed in AgNO₃ solution. These results indicate that during electron irradiation, the microvoids with size ≥3 Å were retained in the surface region through which silver atoms of size ～2.88 Å could diffuse into the polyimide. The average depth of diffusion of silver atoms in the polyimide was ～2.5 μm.     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.     

Effect of electron irradiation on excess currents of GaSb tunnel diodes

Forward biased currents in GaSb tunnel diodes are studied. In the excess current region four segments with differing current transfer mechanisms can be distinguished in the forward branch of the current-voltage curve (CVC) for unirradiated diodes. Irradiation by electrons with energies of 2.2 MeV produces an increase in excess current accompanied by a change in the current transfer mechanisms in the individual segments. The increase in excess current is related to formation and realignment of radiation defects which produce shallow and deep levels in the GaSb forbidden zone. Tunnel spectroscopy with irradiation was used to determine energy levels of E_c-0.060 and E_c –0.2 eV in the n-region of the p-n junction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 89–93, July, 1984.     

Effect of electron and gamma irradiation on elastic characteristics of KTiOPO4 crystals

The elastic moduli C ₁₁ and C ₃₃ of KTiOPO₄ crystals unirradiated and irradiated by electrons and gamma quanta in the temperature range 100–330 K have been measured by the echo-pulse technique. It has been shown that C ₁₁ < C ₃₃ and, with increasing temperature, their values smoothly decrease; moreover, in the temperature range of the second-order phase transition at T ～ 281 K, the curves C ₁₁ = f(T) and C ₃₃ = f(T) exhibit anomalies in the form of a kink. It has been established that, under electron irradiation, the elastic moduli decrease and the phase transition temperature increases. Irradiation of KTiOPO₄ crystals by gamma quanta with a dose of 10⁷ R has no substantial effect on the dynamic characteristics of this crystal.     

Automatic measurement of the creep behavior of linear polymers in the course of homogeneous drawing

An automatic device was built, enabling the creep behavior of fibers of linear semicrystalline polymers to be studied during various stages of homogeneous drawing. The device first deforms the sample at constant speed up to a certain draw ratio; then, without interrupting the stress, the character of deformation is changed from deformation at constant speed to that caused by constant load (creep). It was verified that the method described supplies more detailed information on the changes of the mechanical behavior of polymers at various stages of orientation than does the more conventional stress-strain curve.     

Effect of fast electron irradiation on the electroluminescence spectrum of GaP:N p-n structures

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 49, No. 5, pp. 785–789, November, 1988.     

Effect of substrate interactions on the melting behavior of thin polyethylene films

Polymer films have been known to change their physical properties when film thickness is decreased below a certain value. The cause of this phenomenon is still unclear but it has been suggested that interactions and/or chain free-volume changes at the surface of the films are largely responsible for this behavior. In this paper, the effect of substrate interactions on the behavior of polymer thin films is evaluated quantitatively. The infrared spectra of nanothin polyethylene (PE) films were recorded as a function of temperature and amount of substrate covering the surface of the film. The evolution of specific bands in the CH₂ rocking region of the spectra was used to determine the melting temperature (T _m ) of the material. Results show different variations in T _m depending on the nature of the substrate, indicating that interactions dominate free-volume considerations in PE thin films. By varying the amount of surface coverage, a quantitative estimate of the heat of interaction was determined, which confirmed the importance of surface interactions.