High-purity carbon nanotubes (CNTs) are produced by chemical vapour deposition of camphor, an environment-friendly hydrocarbon. In a small CVD reactor (1-m long and 26- mm wide), CVD of 3 g camphor at 650°C for 1...
In this study, Lonza Corporation's PT-15 cyanate ester (CE), a low viscosity, high performance resin system was used with two types of silicon carbides (SiC): nano-SiC particles and nano-SiC whiskers, as well as m...
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ISBN:
(纸本)1563478927
In this study, Lonza Corporation's PT-15 cyanate ester (CE), a low viscosity, high performance resin system was used with two types of silicon carbides (SiC): nano-SiC particles and nano-SiC whiskers, as well as multi-wall carbon nanotubes (buckytubes) to create new types of cyanate ester-SiC and cyanate ester-buckytube nanocomposites. High shear mixing techniques were used to uniformly disperse the n-SiC particles, n-SiC whiskers, and buckytubes in the cyanate ester resin matrix. Several processing parameters such as mixing speed and mixing duration were examined to produce optimal uniform dispersions of nanoparticles into the resin matrix. Polymer nanocomposites morphological microstructures were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to determine whether n-SiC particles/n-SiC whiskers/buckytubes are distributed uniformly within the polymer matrix. Thermogravimetric analysis (TGA) was used to study the thermal stability of these nanocomposites. Differential scanning calorimeter (DSC) was used to determine the Tg of the polymer nanocomposites. All levels of n-SiC particles dispersed well in the CE resin. The 10% n-SiC particle gave the best enhancement of thermal stability. All loadings of n-SiC whisker did not exhibit any thermal stability enhancement to the CE resin. Phase separation was observed for all loading levels of CE-buckytubes specimens. Buckytube failed to disperse uniformly in the PT-15 CE because of processing limitations and fundamental material incompabiltiy. Functionalization of the buckytube is recommended to enhance uniform dispersion in the PT-15 CE resin.
We report the stepwise assembly of europium oxide (Eu2O3) nanocrystals into one dimensional europium hydroxychloride (Eu(OH)2Cl) nanostructures. Synthesized via a simple colloidal chemistry procedure, the Eu2O3 nanocr...
We report the stepwise assembly of europium oxide (Eu2O3) nanocrystals into one dimensional europium hydroxychloride (Eu(OH)2Cl) nanostructures. Synthesized via a simple colloidal chemistry procedure, the Eu2O3 nanocrystals organized into anisotropic nanoneedles and nanospindles via solution‐phase heat treatment. Transmission electron microscopy (TEM) revealed the shape and crystalline arrangement of the nanostructures.
In this study, stable air/liquid interfaces and high-aspect ratio polymer micro membranes with complex and controlled structures were formed within microfluidic channels. The air/liquid interfaces were formed at hydro...
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In this study, stable air/liquid interfaces and high-aspect ratio polymer micro membranes with complex and controlled structures were formed within microfluidic channels. The air/liquid interfaces were formed at hydrophilic/hydrophobic boundaries defined by patterned and alkanethiols treated Cu surfaces. The two-phase interfaces were further utilized for interfacial polymerization with two immiscible liquid phases containing the reagents for polymer membrane in the microchannel, to generate polymer micro membranes with not only complex in-plane shapes but also z-direction configurations. To demonstrate this method, high quality and complex nylon membranes were fabricated in microchannels. Straight membranes as long as 15mm, 50 mum thick and 500 mum tall in a microfluidic channel were successfully fabricated, and membranes with different structures were realized.
X-ray magnetic circular dichroism (XMCD) measurements and density functional theory (DFT) are used to study the electronic conduction states in Gd5(Ge1−xSix)4 materials through the first-order bond-breaking magnetostr...
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X-ray magnetic circular dichroism (XMCD) measurements and density functional theory (DFT) are used to study the electronic conduction states in Gd5(Ge1−xSix)4 materials through the first-order bond-breaking magnetostructural transition responsible for their giant magnetocaloric effect. Spin-dependent hybridization between Ge 4p and Gd 5d conduction states, which XMCD senses through the induced magnetic polarization in Ge ions, enables long-range Ruderman-Kittel-Kasuya-Yosida ferromagnetic interactions between Gd 4f moments in adjacent Gd slabs connected by Ge(Si) bonds. These interactions are strong below but weaken above the Ge(Si) bond-breaking transition that destroys 3D ferromagnetic order.
The propagation of heat pulses in zigzag and armchair double wall nanotubes (DWNTs) has been investigated using molecular dynamics simulations. It is found that the leading heat wave packets in zigzag (9,0)∕(18,0) an...
The propagation of heat pulses in zigzag and armchair double wall nanotubes (DWNTs) has been investigated using molecular dynamics simulations. It is found that the leading heat wave packets in zigzag (9,0)∕(18,0) and armchair (5,5)∕(10,10) DWNTs move with the speed of longitudinal acoustic (LA) phonon modes. The intensities of the leading heat wave packets in outer and inner shells in DWNTs were found to be five to seven times larger than that of the corresponding single wall nanotubes (SWNTs). The heat energy carried by the leading heat wave packets in zigzag DWNT was about four and five times more than those in armchair DWNT shells. Within the leading LA wave packet, the strain in the inner shell of the DWNTs is stronger than the strain in the outer shell and considerably larger than strain in the corresponding SWNTs. The regions with the largest strain coincide with the regions of high kinetic temperatures within the LA mode wave packets. The higher energy of the LA mode waves in DWNT shells compared to SWNT is attributed to the presence of higher strain fields in DWNTs compared to individual SWNTs. The higher strain in the inner shell of DWNT compared to the outer shell accounts for the three to five times higher kinetic energy of leading wave packets in inner shells compared to those in outer shells. The induced strain fields in zigzag DWNT are distributed over a wider region compared to armchair DWNT, and the strains in inner and outer shells of zigzag DWNT are out phase by 180°.
The first-order antiferromagnetic to ferromagnetic phase transition in Gd5Ge4 becomes arrested at low temperatures in a certain range of applied magnetic fields. This effect gives rise to a low temperature magnetic-gl...
The first-order antiferromagnetic to ferromagnetic phase transition in Gd5Ge4 becomes arrested at low temperatures in a certain range of applied magnetic fields. This effect gives rise to a low temperature magnetic-glass state in Gd5Ge4. Here we report results of dc magnetization measurements investigating the static and dynamic magnetic properties of this low temperature magnetic-glass state. The process of devitrification (or de-arrest) of this magnetic glass is studied by varying both magnetic field and temperature. This devitrification process has quite distinct and separate signatures compared to the process of the magnetic-glass formation. Furthermore, the results of our experimental study support the recently introduced phenomenological idea of correlation between the supercooling of the antiferromagnetic phase and the kinetic arrest of the antiferromagnetic to ferromagnetic phase transition.
We have used Bragg rod x-ray diffraction combined with a direct method of phase retrieval to extract atomic resolution electron-density maps of a complementary series of heteroepitaxial III-V semiconductor samples. Fr...
We have used Bragg rod x-ray diffraction combined with a direct method of phase retrieval to extract atomic resolution electron-density maps of a complementary series of heteroepitaxial III-V semiconductor samples. From the three-dimensional electron-density maps we derive the monolayer spacings, the chemical compositions, and the characteristics of the bonding for all atomic planes in the film and across the film-substrate interface. InAs films grown on GaSb(001) under two different As conditions (using dimer or tetramer forms) both showed conformal roughness and mixed GaAs∕InSb interfacial bonding character. The As tetramer conditions favored InSb bonding at the interface while, in the case of the dimer, the percentages corresponding to GaAs and InSb bonding were equal within the experimental error. The GaSb film grown on InAs(001) displayed significant In and As interdiffusion and had a relatively large fraction of GaAs-like bonds at the interface.
The surface dynamics of supported ultrathin polystyrene films with thickness comparable to the radius of gyration were investigated by surface sensitive x-ray photon correlation spectroscopy. We show for the first tim...
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The surface dynamics of supported ultrathin polystyrene films with thickness comparable to the radius of gyration were investigated by surface sensitive x-ray photon correlation spectroscopy. We show for the first time that the conventional model of capillary waves on a viscous liquid has to be modified to include the effects of a shear modulus in order to explain both static and dynamic scattering data from ultrathin molten polymer films.
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