Three different kinds of siloxane-containing polybenzamide copolymers have been prepared: a series of siloxane-containing segmented copolymers; a siloxane-poly(benzamide) random copolymer; and a poly(benzamide) - poly...
Three different kinds of siloxane-containing polybenzamide copolymers have been prepared: a series of siloxane-containing segmented copolymers; a siloxane-poly(benzamide) random copolymer; and a poly(benzamide) - poly(dimethylsiloxane) block copolymer. The structures of these copolymers were confirmed using diffuse reflectance FTIR spectroscopy. Dilute solution viscometery showed them to be high polymers. The thermal stabilities of these copolymers were studied using thermal gravimetric analysis. Incorporation of siloxane units via a phenyl link was found to not affect the inherent thermal stability of the poly(benzamide) chain. The solution phase behavior of these copolymers in DMAC/LiCl was studied using an optical microscope fitted with cross-polars. The segmented copolymers and the block copolymer exhibited lyotropic behavior, which was influenced by the amount of siloxane and the overall molecular architecture. Solutions of the random copolymer were isotropic at all concentrations studied.
Novel polyurethane (PU) conducting films consisting of hydroxyl-terminated polybutadienes (HTPB) and carboxyl functionalized multi-walled carbon nanotubes (MWNTs-COOH) were developed by a simple coupling approach base...
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The photoinduced dynamical reverse piezoelectric effect in epitaxial BiFeO3 thin films has been characterized by time-resolved hard X-ray diffraction measurements for ultrafast optical control of room temperature mult...
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The combination of polymer/clay nanocomposites with the gas dissolution microcellular foaming process is expected to yield materials with combined advantages of both techniques. One of the most important advantages ex...
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The combination of polymer/clay nanocomposites with the gas dissolution microcellular foaming process is expected to yield materials with combined advantages of both techniques. One of the most important advantages expected is the gas barrier role that nanoclays would play in the polymer matrix. The gas dissolution process turns to be a good way to study both this gas barrier effect and the microcellular foamability of these composites. From this point of view, CO2 diffusion coefficient has been obtained for polyethylene matrices containing 3% and 5% nanoclays. After that, samples with and without nanoparticles were foamed and morphologically characterized. A nucleating effect of the clays has been detected in the early stages of foaming.
We show evidence of electrical and thermal conductivity percolation in polymer based carbon nanotube (CNT) composites, which follow power law variations with respect to the CNT concentrations in the matrix. The experi...
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Oxidation tests were performed isothermally at 1000°C on chill block melt spun metallic ribbons with alloy compositions consisting of Ni(46–50 at%), Al(31–33 at%), Co(17–20 at%) and Hf(0–1 at%). The oxidation...
Oxidation tests were performed isothermally at 1000°C on chill block melt spun metallic ribbons with alloy compositions consisting of Ni(46–50 at%), Al(31–33 at%), Co(17–20 at%) and Hf(0–1 at%). The oxidation rates were calculated and the microstructure was examined. Results indicated the difference in microstmctural and oxidation characteristics could largely be attributed to the differences in the superheat of the melt. There was no indication that hafnium retarded grain growth. The oxidation behavior of two of the ribbons exhibited a logarithmic rate law.
Oxidation behavior of binary Ti-48Al and ternary alloys with 1.5 at.% Cr, 1.4 at.%Mn, 0.2 at.% W, 2.2 at% V, 20 vol.% TiNb particles were examined in an air atmosphere at 704°C, 815°C and 982°C. Results...
Oxidation behavior of binary Ti-48Al and ternary alloys with 1.5 at.% Cr, 1.4 at.%Mn, 0.2 at.% W, 2.2 at% V, 20 vol.% TiNb particles were examined in an air atmosphere at 704°C, 815°C and 982°C. Results indicate that the addition of Cr is detrimental at all temperatures. The Cr and V containing alloys exhibited a linear oxidation behavior at 815°C while the Mn containing alloy showed a linear behavior at 982°C. At 982 °C the alloys with W and V exhibit the best oxidation behavior. The mechanism of oxidation has been explained with the help of a simple vacancy model for oxygen diffusion.
A wide information gap exists between our present atomic-scale knowledge of metal oxidation derived from conventional ultrahigh vacuum (UHV) surface science experiments and the oxidation mechanisms obtained from the g...
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A wide information gap exists between our present atomic-scale knowledge of metal oxidation derived from conventional ultrahigh vacuum (UHV) surface science experiments and the oxidation mechanisms obtained from the growth of bulk oxide thin films under technologically relevant realistic (or near-) atmospheric conditions. To bridge this pressure gap, we present an in-situ transmission electron microscopy (TEM) study of the initial oxidation stage of Cu(100) and Cu-Au(100) surfaces where the oxygen partial pressure varies from 5x10-4 to 150 Torr. For Cu(100), with increasing oxygen partial pressure (pO2), the nucleation density of the oxide islands increases and so does the growth rate of the oxide islands. As the pO2 continues to increase, a transition from epitaxial cube-on-cube Cu2O islands to randomly oriented oxide islands is observed. A kinetic model based on the classic heterogeneous nucleation theory is developed to explain the effect of oxygen partial pressure on the oxide orientation. It is shown that such a transition in the oxide nucleation orientation is related to the effect of oxygen pressure on the nucleation barrier and atom collision rate. The Cu-Au(111) alloy revealed the same oxygen pressure dependency of the oxide nucleation orientation as pure Cu oxidation.
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