Dielectric property and electromagnetic interference shielding effectiveness of ethylene vinyl acetate‐based conductive composites: Effect of different type of carbon fillers

Carbon black, short carbon fiber (SCF), and multiwall carbon nano‐tube (MWNT)‐filled conductive composites were prepared from ethylene vinyl acetate copolymer. The dielectric property and electromagnetic interference (EMI) shielding of carbon black, MWNT, and SCF‐filled composites were studied with different filler loadings. The dielectric constant and loss of filled polymer composites is due to the formation of interfacial polarization in the polymer matrix. It was found that the dielectric constant, dielectric loss, and EMI shielding of filled composites depends on amount and type of filler loading. The results of different experiments have been discussed in the light of break down and formation of continuous conductive network in polymer matrix. The results indicate that these composites can be used as effective EMI shielding materials. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers.     

High‐performance EMI shielding materials based on short carbon fiber‐filled ethylene vinyl acetate copolymer,acrylonitrile butadiene copolymer,and their blends

The composites of carbon fiber with EVA, NBR, and their blends have been made by melt mixing technique. Stress–strain plots of different composites show that the necking phenomenon is increasing with the increase in fiber concentration in the polymer matrix. The scanning electron microscopic analysis and swelling study exhibit poor interaction between the short carbon fiber and polymer matrix. The decrease in DC resistivity with the increase in short carbon fiber concentration has been explained on the basis of percolation theory. EMI SE increases slightly with the increase in frequency of electromagnetic radiation but increases sharply with the increase in fiber concentration. EMI SE also depends on blend composition and increases with the increase in EVA concentration in the blend. Return loss is decreasing but absorption loss is increasing with the increase in fiber loading. A linear relationship is observed between the EMI SE and thickness of the composites. The EMI SE is found to increase exponentially with the increase in conductivity of the composite. The permeability value is decreasing with the increase in frequency as well as fiber loading. Thermal properties of the composites have been evaluated by thermogravimetric analysis and dynamic mechanical analysis. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Freeze extrusion fabrication of 13–93 bioactive glass scaffolds for bone repair

A solid freeform fabrication technique, freeze extrusion fabrication (FEF), was investigated for the creation of three-dimensional bioactive glass (13–93) scaffolds with pre-designed porosity and pore architecture. An aqueous mixture of bioactive glass particles and polymeric additives with a paste-like consistency was extruded through a narrow nozzle, and deposited layer-by-layer in a cold environment according to a computer-aided design (CAD) file. Following sublimation of the ice in a freeze dryer, the construct was heated according to a controlled schedule to burn out the polymeric additives (below ~500°C), and to densify the glass phase at higher temperature (1 h at 700°C). The sintered scaffolds had a grid-like microstructure of interconnected pores, with a porosity of ~50%, pore width of ~300 μm, and dense glass filaments (struts) with a diameter or width of ~300 μm. The scaffolds showed an elastic response during mechanical testing in compression, with an average compressive strength of 140 MPa and an elastic modulus of 5–6 GPa, comparable to the values for human cortical bone. These bioactive glass scaffolds created by the FEF method could have potential application in the repair of load-bearing bones.     

Low power resistive switching memory using Cu metallic filament in Ge0.2Se0.8 solid-electrolyte

Bipolar resistive switching memory device using Cu metallic filament in Au/Cu/Ge_0.2Se_0.8/W memory device structure has been investigated. This resistive memory device has the suitable threshold voltage of V_th > 0.18 V, good resistance ratio (R_High/R_Low) of 2.6 × 10³, good endurance of >10⁴ cycles with a programming current of 0.3 mA/0.8 mA, and 5 h of retention time at low compliance current of 10 nA. The low resistance state (R_Low) of the memory device decreases with increasing the compliance current from 1 nA to 500 μA for different device sizes from 0.2 μm to 4 μm. The memory device can work at very low compliance current of 1 nA, which can be applicable for extremely low power-consuming memory devices.     

Induced Aggregation of AIE‐Active Mono‐Cyclometalated Ir(III) Complex into Supramolecular Branched Wires for Light‐Emitting Diodes

Aggregation‐induced emission (AIE) is commonly observed in irregular bulk form. Herein, unique aggregation properties of an AIE‐active complex into branched supramolecular wires are reported for the first time. Mono‐cyclometalated Ir(III) complex shows in‐plane J‐aggregation at the air–water interface owing to the restriction of intramolecular vibration of bidentate phenylpyridinato and intramolecular rotations of monodentate triphenylphosphine ligands at air–water interface. As a consequence, a large enhancement of luminescence comparable to the solid state is obtained from the monolayers of supramolecular wires. This unique feature is utilized for the fabrication of light‐emitting diodes with low threshold voltage using supramolecular wires as active layer. This study opens up the need of ordered assembly of AIE complexes to achieve optimal luminescence characteristics.     

Modeling of DC conductivity for ethylene vinyl acetate (EVA)/polyaniline conductive composites prepared through insitu polymerization of aniline in EVA matrix

Ethylene vinyl acetate (EVA)/polyaniline (Pani) composites were prepared by insitu polymerization technique. DC and AC conductivity of the composites have been investigated. Different theoretical models like Voet, Scarisbrick, Bueche, and McCullough have been applied to predict DC conductivity of the composite systems. Scarisbrick model exhibits somewhat similarity between experimentally observed and theoretically predicted conductivity. The limitations of the models as well as the deviations between the theoretically predicted and experimentally observed results have been discussed. A new model for conductivity has been proposed which fit well with the experimentally observed results.     

Direct‐current conductivity at a cryogenically low temperature for polymer/carbon composites: Applicability of different theoretical models

In this study, we focused on the behavior of the direct‐current (dc) conductivity/resistivity in a cryogenically low temperature region (10–300 K) for ethylene vinyl acetate copolymer, acrylonitrile butadiene copolymer, and their 50/50 blend composites filled with different conductive carbons. The composites were prepared through a melt‐mixing technique. Different behaviors of the dc resistivity/relative resistivity for the composites were observed; these behaviors depended on the nature of the polymers, the filler types, and the filler concentration when plotted with respect to the temperature. The results of dc conductivity were fitted with some existing theoretical models, including Arrhenius, Kivelson, and Mott's variable range hopping, to check their applicability for these composite systems. We observed that none of the models was applicable within the entire range of measurement temperatures but were confined within limited temperature ranges. The reason behind the nonapplicability of the models is discussed with consideration of their drawbacks and limitations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43541.     

Performance modeling and analysis of carbon nanotube bundles for future VLSI circuit applications

In this work, we have presented a comprehensive analysis of the performance of copper (Cu) and existing carbon nano tube (CNT) bundle structures (i.e. SWCNT, DWCNT and MWCNT) across nanometer technology nodes like 45, 32, 22 and 16 nm at local, intermediate and global level interconnects. Double walled carbon nano tubes (DWCNTs) and multi walled carbon nano tubes (MWCNTs) are modeled like simple single walled carbon nano tube (SWCNT) equivalent model with high accuracy. The analytical closed form delay expressions for SWCNT, DWCNT and MWCNT bundles have been found out. It has been observed that sparse SWCNT bundle interconnects show about 50 % performance improvement for 20 \(\upmu \) m long local level interconnects over Cu in 16 nm technology node, whereas the performance advantage numbers for MWCNT and sparse DWCNT bundles are 50 and 35 % respectively. For 200 \(\upmu \) m long intermediate level interconnects, the performance advantage numbers are 85, 80 and 75 % for dense SWCNT, MWCNT and dense DWCNT bundles respectively in 16 nm node. For 10 mm long global level interconnects, the performance advantage numbers are 85, 85 and 75 % for dense SWCNT, MWCNT and dense DWCNT bundles respectively in 16 nm node. It is also observed that the performance numbers improve with scaling for all levels of interconnects. It is also shown that the ratio of delay of CNT bundles and Cu for various levels of interconnects agree well with the existing work.