共查询到20条相似文献,搜索用时 15 毫秒
1.
K. Hareesh C. Ranganathaiah P. Ramya R. Bhargavi Geetha G. Nair Sangappa Ganesh Sanjeev 《应用聚合物科学杂志》2013,127(3):2010-2018
The modifications in microstructural, optical, and photoluminescence properties of the Lexan polycarbonate (bisphenol‐A‐polycarbonate) films exposed to different electron doses have been studied using UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), positron annihilation lifetime spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The obtained UV–vis spectroscopy results showed decrease in optical energy gap, optical activation energy, and increase in number of carbon atoms per cluster with increase in electron dose. The chemical changes in electron irradiated polymers due to chain scission and reconstruction have been observed from FTIR spectroscopy. The correlation of positron lifetime study with optical measurement is obtained, and electron irradiation‐induced microstructural modifications within the polymer is understood. SEM result shows the degradation of Lexan polymer after electron irradiation. The mechanical properties and average molecular weight of Lexan decrease after irradiation, whereas average number of chain scissions per original polymer molecule increases. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
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Outdoor degradation of isotactic polypropylene (PPI) plates was studied by means of positron annihilation lifetime spectroscopy (PALS), absorption infrared spectroscopy, differential scanning calorimetry (DSC) and density measurements. Infrared spectra reveal the presence of oxygenated species into the exposed polymer induced by external agents. Results from thermal and density analysis suggest an increase of crystallinity of the sample with exposure time. Positron data strengthen such a conclusion, showing a reduction of the amorphous zones as monitored by the corresponding decrease of positronium (Ps) formation. Furthermore, an estimation of the average sizes of the free volume holes and of the defects in the crystalline regions was obtained. 相似文献
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F. H. Scholes S. A. Furman A. E. Hughes A. J. Hill F. Tuomisto K. Saarinen S. J. Pas 《Journal of Coatings Technology and Research》2006,3(2):105-108
A chromate-inhibited primer has been characterized by Doppler broadening energy spectroscopy (DBES), scanning electron microscopy
(SEM), and Raman spectroscopy. The S-parameter obtained by DBES exhibited a three-layer depth profile, which is attributed
to the presence of a “skin” layer in the polymer matrix of the primer and a concentration gradient in the inorganic phases
distributed through the primer. The primer was also examined by DBES following immersion in solution. The change observed
in the S-parameter upon immersion indicated water filling the molecular free volumes in the primer. The ability to monitor
the depth of water uptake as a function of immersion time illustrates that the primer does not need to be fully saturated
for chromate release to occur. 相似文献
5.
Fourier‐transform infrared spectroscopic study of plasticization effects on the photodegradation of poly(fluorostyrene) isomers films
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The photodegradation of poly(fluorostyrene) isomers with different amounts of phthalate and terephthalate plasticizers has been investigated with the aid of Fourier‐transform infrared spectroscopy. Photo irradiation was carried out with light from a Hydrogen‐Xenon lamp at 265 nm and 293 K. As irradiation time increased, changes occurred in the structure of the polymers due to the destruction of polymeric chains and the formation of new photo products during the degradation. The photo products caused shifts, an increase or decrease of the polymer vibrational frequencies, as well as changes in numerous infrared band intensities. The increase in the intensities of the analyzed ranges is attributed to the formation of carbonyl, hydroxyl, and aliphatic ketones and to the increase in the number of polyene structures that resulted from hydrogen abstraction during photodegradation reactions. The analysis of the Fourier‐transform infrared spectra of the irradiated and nonirradiated samples showed a noticeable formation of a new broad band centered at (1,727 cm?1, C=O), assigned to the growth of aliphatic ketones formerly from the reaction of reactive alkoxy radicals. Its intensity was found to increase with the increase in irradiation time and also with the increase in the amount of added terephthalate and phthalates plasticizer, indicating an increase in the efficiency of the photo degradation process. Trends of photostability of these isomers were found such that poly(para‐fluorostyrene) > poly(meta‐fluorostyrene) > poly(ortho‐fluorostyrene). The photodegradation process for these plasticized isomers was found to increase by the increase in the bulkiness of the plasticizer molecule . J. VINYL ADDIT. TECHNOL., 24:75–83, 2018. © 2015 Society of Plastics Engineers 相似文献
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《Journal of Adhesion Science and Technology》2013,27(6):425-437
Positron annihilation lifetime spectra were measured on glass bead-filled high density polyethylene, with a glass content ranging from 0 to 50% by volume. In some cases, the glass beads were surface-modified by different amounts of an azidofunctional alkoxysilane. A composite model for positron annihilation was proposed to account for the observed changes in the relative intensities with increasing amount of filler. A decrease in the intensity of the longest lifetime with increased amount of the silane coupling agent was observed. This suggests a reduction of the free volume in the interphase region between glass and polyethylene, despite a reduction in the crystallinity of the interphase. 相似文献
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X-ray diffraction, positron annihilation, electron microscopy and bulk density measurements are reported as a function of the degree of acetylation for a linters cotton. Heterogeneous reaction proceeds with a retention of ordered structure in the fibers. Substitution does increase the extent of disorder but is not sufficiently extensive to disrupt completely order at the fiber, fibril, micro fibril, and crystallite levels. The generation of disorder is associated with an increase in the interfibrillar distance, a breakup of the microfibrillar structure without a total disruption of the microcrystalline structure. 相似文献
8.
G. Spathis 《Polymer》2008,49(20):4462-4468
In this work, yielding and post yielding effects are analyzed using the idea of the inhomogeneous distribution of strain in polymers under deformation. This idea is directly connected with the free volume concept, as created in the polymeric bulk during the frozen in process, and or the density fluctuations combined with other type defects. A simple strain density distribution function is assumed, following experimental results available from techniques such as positron annihilation lifetime spectroscopy (PALS). Hereafter, a functional form of the rate of plastic deformation is extracted, which will be combined with a given kinematic formulation. The proposed analysis is tested with experimental data of polystyrene (PS) and PS/SiO2 nanocomposites. The incorporation of nanosized fillers into the polymeric bulk, strongly affects the free volume distribution and/or the distribution of defects related with density fluctuations. This fact is reflected in the model parameter values, and their variation in respect to the different material types. With the proposed analysis, it has been proved that all features of yield process, including strain softening and strain hardening effect are easily described. 相似文献
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The effect of ultraviolet (UV) radiation on the structure and performance of hydrogenated nitrile butadiene rubber (HNBR) was studied in this paper. The HNBR was exposed to UV radiation for various durations (0, 7, 14, 21 and 28 days). The Fourier transform infrared spectroscopy (FTIR) results demonstrated that the surface molecular structures were oxidized to generate oxygenated species under UV radiation. The oxidative degree enhanced with the increase of aging time, resulting in thicker and denser cracks on the surface. The plausible aging mechanism of HNBR was suggested. The free volume of HNBR before and after UV aging was characterized by positron annihilation lifetime spectroscopy (PALS) and their cross-linking density, compression set, mechanical and gas permeability properties were also analyzed. In the first 14 days of UV irradiation, the dominant chain-scission reaction led to a decrease in cross-linking density of HNBR, resulting in the enhancement of free volume and thereby the increase of gas permeability. When the aging time was longer than 14 days, cross-linking reaction played a leading role and the free volume decreased, thus causing the reduction of gas permeability. As the aging time increased, the glass transition temperature (Tg), tensile strength and storage modulus of HNBR initially reduced and then increased, which was in agreement with the changing trend of cross-linking density. 相似文献
10.
Silviu Jipa Radu Setnescu Traian Zaharescu Tanta Setnescu Mustapha Kaci Naima Touati 《应用聚合物科学杂志》2006,102(5):4623-4629
The analysis of the chemiluminescence (CL) kinetic parameters (induction time, oxidation rate, and activation energy) after the UV irradiation and outdoor exposure of isotactic polypropylene (i‐PP) films have been studied. The initial CL emission intensity increased with increasing photodegradation time of i‐PP films. On photodegradation, the activation energies were found to decrease linearly with time of UV‐irradiation and outdoor exposure. The slopes of these linear dependences were used to indicate the degree of photodegradation of the polymer and also for the characterization of the stabilizing effect of the additive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4623–4629, 2006 相似文献
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Graphene nanosheets-supported Sn-Pt bimetallic nanoparticles (GNs/Sn-Pt) were prepared by precipitation method. The obtained GNs/Sn-Pt was used as a photocatalyst for photodegradation of Basic Green 5 (BG5) in aqueous solution under sunlight. The morphology and photodegradation study was performed by SEM and UV–VIS spectrophotometry, respectively. The SEM image showed the presence of Sn and Pt on GNs, being confirmed by energy dispersive X-ray (EDX) analysis. The photodegradation study of BG5 showed that the dye degradation increases as a function of irradiation time. The degradation of BG5 was found to be pH dependent and maximum degradation was found at higher pH. 相似文献
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D. V. Petrov A. S. Dyukareva T. V. Antropova V. P. Veiko G. K. Kostyuk E. B. Yakovlev 《Glass Physics and Chemistry》2003,29(5):456-460
The kinetics of surface sintering of flat plates of the 96SiO2 · 3.8B2O3 · 0.2Na2O (mol %) porous glass exposed to CO2 laser radiation is investigated under conditions when either the irradiation time is varied at a constant radiation power density or the radiation power density is varied at a constant irradiation time. It is established that the irradiation time is the most appropriate controlled parameter in the process of sintering. A decrease in the thickness of the porous layer sintered on the plate surface is accompanied by an increase in the radii of curvature of the interfaces of this layer. 相似文献
13.
《国际聚合物材料杂志》2012,61(3-4):313-318
Abstract Structural rearrangements in glassy PMMA on polymer plastic deformation and recovery of residual plastic deformation in glassy state were studied by positron annihilation lifetime spectroscopy. Uniaxial compression was shown to be accompanied by a decrease in concentration of free volume microregions in disordered polymer regions, which were characterized by low packing density. Recovery of residual deformation at elevated temperatures but below glass transition point Tg proceeds without any noticeable changes in fractional content of free volume both in disordered and ordered polymer regions. The advantages of positron annihilation lifetime spectroscopy for studying microstructure and structural rearrangements in polymers were discussed. 相似文献
14.
We report, for the first time, our result on characterisation of Al-pillared clay using positron annihilation spectroscopy (PAS) along with XRD and BET techniques. Positron life-time spectra for Al-pillared montmorillonite, as received and calcined at different temperature (100–500°C), along with the parent natural clay are measured. The annihilation rate of ortho-positronium (o-Ps) increases monotonically with calcination temperature up to 300°C and falls subsequently. Similar behaviour is seen for the fraction of o-Ps formed. We interpret the initial rise in annihilation rate of o-Ps to be due to the increase in Brønsted acidity with dehydroxylation of pillars. The reduction in annihilation rate on calcination at higher temperatures could be due to loss of acidity and/or due to mesopore formation following delamination of clay structure. 相似文献
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《Diamond and Related Materials》1999,8(7):1214-1219
Amorphous hydrogenated carbon nitride [a-C:H(N)] films were deposited from the mixture of C2H2 and N2 using the radio frequency plasma enhanced chemical vapor deposition technique. The films were characterized by X-ray photon spectroscopy, infrared, and positron annihilation spectroscopy. The internal stress was measured by substrate bending method. Up to 9.09 at% N was incorporated in the films as the N2 content in the feed gas was increased from 0 to 75%. N atoms are chemically bonded to C as C–N, CN and CN bond. Positron annihilation spectra shows that density of voids increases with the incorporation of nitrogen in the films. With rising nitrogen content the internal stress in the a-C:H(N) films decrease monotonically, and the rate of decrease in internal stress increase rapidly. The reduction of the average coordination number and the relax of films structure due to the decrease of H content and sp3/sp2 ratio in the films, the incorporation of nitrogen atoms, and the increases of void density in a-C:H(N) films are the main factors that induce the reduction of internal stress. 相似文献
17.
Angular correlations of positron annihilation gammas were applied to study NaHY zeolite catalysts whose acidity was altered by an ion-exchange process. The Brønsted acidity was found to vary linearly with the lineshape parameter of the angular correlation spectrum of the sample. 相似文献
18.
Dorota Chelminiak-Dudkiewicz Aleksander Smolarkiewicz-Wyczachowski Katarzyna Wegrzynowska-Drzymalska Marta Ziegler-Borowska 《International journal of molecular sciences》2022,23(5)
Levan, as a biocompatible and renewable biopolymer with anticancer properties, is a promising candidate for a wide range of applications in various fields of industry. However, in the literature, there is a lack of information about its behavior under the influence of UV irradiation, which may limit its potential application, including medical science. Therefore, this study describes the effects of irradiation on the structural properties of levan. This type of fructan was subjected to stability tests under radiation conditions using LED and polychromatic lamps. The results showed that the photodegradation of levan irradiated with a polychromatic light occurs faster and more efficiently than the photodegradation of levan irradiated with an LED lamp. Furthermore, AFM analysis showed that the surface became smoother after irradiation, as evidenced by decreasing values of roughness parameters. Moreover, UV irradiation causes the decrease of total surface free energy and both its components in levan; however, more significant changes occur during irradiation of the sample with a polychromatic lamp. 相似文献
19.
Structural relaxation processes are reported in polystyrene as a function of ageing time using positron annihilation lifetime and Doppler broadening spectroscopy. Changes in the intensity, lifetimes and line shapes with increasing temperature for ortho positronium annihilation show an internal consistency between the two experiments and may be described in terms of a simple logarithmic decay process. The isochronous and isothermal ageing data show internal consistency and are best described by either a Narayanaswamy distribution or a double exponential fit of the data. The possible effects of charging during the isothermal decay measurements are explored and found to influence the short term decay behaviour. Measurements of the liquid phase are extrapolated to lower temperatures to allow estimation of the equilibrium lifetimes in the glassy phase. Changes in the lifetimes and the long time component of the intensity are interpreted as being indicative of the structural relaxation process; they are not influenced by the effects of charging and exhibit a good correlation with physical ageing behaviour as determined by other techniques. © 1998 SCI. 相似文献
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Free volume and density gradient widths of the free surface of high molecular mass polystyrene was characterized by use of a pulsed low-energy positron lifetime beam. A density gradient in terms of mass density (g/cm3) versus depth (nm) was obtained from the experimental beam data using a novel approach, yielding a width of the density gradient of approximately 3.5 nm. The procedure accounted for the broadening of the positron implantation probe as a function of energy as well as correcting for the increase in positron implantation depths due to the presence of a lower density at the surface region.Moreover, the spectra in the low implantation energy range were found to contain a long-lived lifetime that yielded very large estimates of the free volume effects at the surface. Accounting for this lifetime in the evaluation procedure, resulted in a much improved agreement with the results of other experimental and theoretical investigations in the literature. 相似文献