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21.
The conductive composites were prepared using two different types of conductive black (Conductex and Printex XE2) filled in
matrices like EVA and NBR and their different blends. The electromagnetic interference shielding effectiveness (EMI SE) of
all composites was measured in the X band frequency range 8–12 GHz. Both conductivity and EMI SE increase with filler loading.
However, Printex black shows higher conductivity and better EMI SE at the same loading compared to Conductex black, and this
can be used as a material having high EMI shielding effectiveness value. The conductivity of different blends with same filler
loading generally found to increase slightly with the increase in NBR concentration. However, EMI SE has some dependency on
blend composition. EMI SE increases linearly with thickness of the sample. EMI SE versus conductivity yields two master curves
for two different fillers. EMI SE depends on formation of closed packed conductive network in insulating matrix, and Printex
black is better than Conductex black in this respect. Some of the composites show appreciably high EMI SE (>45 dB). 相似文献
22.
Pranab C. Bandyopadhyay Tapan K. Chaki Srinath Srivastava Gitindra S. Sanyal 《Polymer Engineering and Science》1980,20(6):441-446
Polystyrene foams have been generated and fabricated into differently shaped structures', by change of steaming period under constant impregnation time and solvent-nonsolvent composition. Optical photomicrographs of samples both plain and wax-copper-coated reveal uniform appearance, distinct grain-boundaries, and random cell size distribution. Dielectric measurements have been made on test specimens cut according to wave-guide size at 9.375 GHz X-band microwave frequency by short-circuited wave-guide method of Smith and Hippel modified by Dakin and Works. Dielectric constants are linear, on direct and semi-log scales in bulk-density and volume-fraction, obeying Weiner's inequalities. Formulae of Landau-Lifshitz, Beer, Maxwell-Wagner, Odelevsky, etc. have been tried. Data fit best with the logarithmic law of Lichtenecker and Rother. Specific polarization is also a true function of density. Dielectric constant vs bulk-density plots of foams resemble dielectric-constant vs fractional-density plots based on the theoretical derivation by Smith for polystyrene compacts, signifying that compacts containing closely-spaced oblong-spherical particles arc physically similar to foams having spherical gas inclusions in plastic structures. Tan δ lying in the range 0.002–0.0038 results from conformational polarization (β-relaxation at room-temperature for wide-angle torsional oscillations of side-groups with co-operative motion from wriggling chains). It is therefore possible for low-loss foam dielectrics suitable for micro-wave applications to be made by this method. 相似文献
23.
Pierre Duchene Salim Chaki Abderrahmane Ayadi Patricia Krawczak 《Journal of Materials Science》2018,53(11):7915-7938
Polymer composite materials are being increasingly used in primary load-bearing structures in several advanced industrial fields such as aerospace vessels, railway wagons and mega-scaled wind turbines where detection of subcritical damage initiation can significantly reduce safety issues and maintenance costs. It is therefore crucial to inspect these composite structures in order to assess their structural health and to ensure their integrity. Non-destructive testing techniques (NDT) are used for this purpose, making it possible to monitor mechanical damage of composite materials under in situ or ex situ service conditions. This paper reviews the capabilities of the most common NDT techniques used to inspect the integrity of composite materials. Each technique has a detection potential and cannot allow a full diagnosis of the mechanical damage state of the material. Thus, depending on the occurring damage mechanism and the conditions of use, one technique will be preferred over another, or several techniques should be combined to improve the diagnosis of the damage state of the structures. 相似文献
24.
Dey Ayan Ghosh Shibashis Bhattacharya Sukriti Chaki Nabendu 《Multimedia Tools and Applications》2020,79(3-4):2555-2576
Multimedia Tools and Applications - Watermarks have long been applied to ensure the authenticity of media contents. Computer software is an intellectual outcome in the digital domain. Therefore, it... 相似文献
25.
Bal Abhishek Banerjee Minakshi Chaki Rituparna Sharma Punit 《Multimedia Tools and Applications》2020,79(39-40):29087-29120
Multimedia Tools and Applications - The diagnosis of dementia, particularly in the early stages is very much helpful with Positron emission tomography (PET) image processing. The most important... 相似文献
26.
Physicochemical and Adhesion Characteristics of High-Density Polyethylene when Treated in a Low-Pressure Plasma under Different Electrodes 总被引:1,自引:0,他引:1
The present investigation studys the effects of different electrodes such as copper, nickel, and stainless steel under low-pressure plasma on physicochemical and adhesion characteristics of high-density polyethylene (HDPE). To estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to low-pressure plasmas have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that the surface energy and its polar component increase with increasing exposure time, attain a maximum, and then decrease. The increase in surface energy and its polar component is relatively more important when the polymer is exposed under a stainless-steel electrode followed by a nickel and then a copper electrode. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by optical microscopy and electron spectroscopy for chemical analysis (ESCA). It is observed that when the HDPE is exposed under these electrodes, single crystals of shish kebab structure form, and the extent of formation of crystals is higher under a stainless-steel electrode followed by nickel and then copper electrodes. Exposure of the polymer under low-pressure plasma has essentially incorporated oxygen functionalities on the polymer surface as detected by ESCA. Furthermore the ESCA studies strongly emphasize that higher incorporation of oxygen functionalities are obtained when the polymer is exposed to low-pressure plasma under a stainless-steel electrode followed by nickel and then copper electrodes. These oxygen functionalities have been transformed into various polar functional groups, which have been attributed to increases in the polar component of surface energy as well as the total surface energy of the polymer. Therefore, the maximum increase in surface energy results in stronger adhesion of the polymer when the polymer is exposed under a stainless-steel electrode rather than nickel and copper electrodes. 相似文献
27.
Ethylene-vinyl acetate (EVA) copolymer (12% vinyl acetate content) is subjected to electron beam irradiation using trimethylolpropane trimethacrylate (TMPTMA) as a radiation sensitizer. Mechanical and electrical studies of these irradiated samples show that the strength properties (tensile strength, elongation at break) are increased with radiation dosage up to an optimum radiation dose and sensitizer level above which the properties begin to deteriorate. Crosslinking of the polymer takes place on irradiation which is attributed to an increased gel content with increasing radiation dose. Compared to the original samples both dielectric constant and dielectric loss factor decrease for samples subjected to irradiation. 相似文献
28.
Sharma J Kakade BA Chaki NK Mahima S Pillai VK 《Journal of nanoscience and nanotechnology》2007,7(6):2139-2150
The role of polyfunctional organic molecules in the synthesis of differently shaped metallic nanostructures and their assembly is investigated. These molecules could be used as spacer ligands and also for surface passivation of nanoparticles, especially with the objective of controlling their electronic and optical properties depending on their length scales. We investigate the role of several such molecules, such as 4-aminothiophenol, tridecylamine, Bismarck brown R and Y, mordant brown, fat brown, chrysoidin (basic orange), and 3-aminobenzoic acid in the synthesis and assembly of various nanoparticles of gold and silver. For example, the use of 4-ATP helps in the formation of rod shaped micelles in aqueous acetonitrile as confirmed by transmission electron microscopy (TEM) suggesting their role as soft templates. In addition, 4-ATP has also been used for the formation of heteroassembly of spherical nanoparticles of gold and silver at controlled pH. Significantly, triangular and hexagonal gold nanoplates are formed at room temperature by similar polyfunctional dye molecule, Bismarck brown R (BBR), while other analogous dye molecules give only arbitrary shaped gold nanoparticles. Further confirmation of their role in shape determination comes from linear amine molecules such as tridecylamine, which give only spherical nanoparticles both for silver and gold. In essence, our study confirms the role of various such organic molecules in shape controlled synthesis of nanoparticles. We also report optical and electrochemical properties of few of these nanostructures as a function of their shape. 相似文献
29.
The electrical and mechanical properties of new conductive rubber composites based on ethylene–propylene–diene rubber, acrylonitrile butadiene rubber (NBR), and their 50/50 (weight ratio) blend filled with conductive black were investigated. The threshold concentrations for achieving high conductivity are explained on the basis of the viscosity of the rubber. The electrical conductivity increases with the increase in temperature whereas the activation energy of conduction decreases with an increase in filler loading and NBR concentration in the composites. The electrical hysteresis and electrical set are observed during the heating–cooling cycle, which is mainly due to some kind of irreversible change occurring in the conductive networks during heating. The mechanisms of conduction in these systems are discussed in the light of different theories. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 887–895, 1999 相似文献
30.
Utpal Basuli Tapan K. Chaki Santanu Chattopadhyay Sunil Sabharwal 《Polymer Composites》2010,31(7):1168-1178
The ethylene methyl acrylate copolymer (EMA) and multiwalled carbon nanotube (MWNT) based composites were prepared by solution mixing as well as by melt processing of the films obtained after solution mixing. Field emission scanning electron microscopy, transmission electron microscopy, and XRD were used to characterize morphologies of various composites. MWNTs were found to be more dispersed in the composites prepared by melt process after solution process. There was no obvious agglomeration of MWNTs at lower % loading (up to 2.5%) in the polymer matrices especially the composites are prepared solution plus melt mixing and consequently better interaction between MWNTs and EMA matrix was anticipated. XRD and differential scanning calorimetry studied showed that the nanotubes affect the crystallization process and subsequently their role as a nucleating agent was established. These are reflected in the mechanical properties of the composites. Dynamic mechanical analysis showed that the storage modulus of the composites drop very sharply beyond 2.5 wt% of MWNT content with increasing % strain and it reflects the Payne effect (a substantial decrease in the storage modulus of a particle‐reinforced polymer with an increase in the amplitude of dynamic oscillations). The influence of concentration of filler was also realized by frequency sweep experiment. The incorporation of MWNTs in EMA offered a stabilizing effect since onset of degradation occurs at higher temperatures for composites. POLYM. COMPOS., 31:1168–1178, 2010. © 2009 Society of Plastics Engineers 相似文献