Synthesis and Characterization of Carbon Nanotube-Polymer Multilayer Structures

We develop lightweight, multilayer materials composed of alternating layers of poly dimethyl siloxane (PDMS) polymer and vertically aligned carbon nanotube (CNT) arrays, and characterize their mechanical response in compression. The CNT arrays used In the assembly are synthesized with graded mechanical properties along their thickness, and their use enables the creation of multilayer structures with low density (0.12-0.28 g/cm(3)). We test the mechanical response of structures composed of different numbers of CNT layers partially embedded in PDMS polymer, under quasi-static and dynamic loading. The resulting materials exhibit a hierarchical, fibrous structure with unique mechanical properties: They can sustain large compressive deformations (up to similar to 0.8 strain) with a nearly complete recovery and present strain localization in selected sections of the materials. Energy absorption, as determined by the hysteresis observed In stress-strain curves, is found to be at least 3 orders of magnitude larger than that of natural and synthetic cellular materials of comparable density. Conductive bucky paper Is Included within the polymer interlayers. This allows the measurement of resistance variation as a function of applied stress, showing strong correlation with the observed strain localization In compression.

Synthesis from zinc oxalate, growth mechanism and optical properties of ZnO nano/micro structures

We report the synthesis of various morphological micro to nano structured zinc oxide crystals via simple precipitation technique. The growth mechanisms of the zinc oxide nanostructures such as snowflake, rose, platelets, porous pyramid and rectangular shapes were studied in detail under various growth conditions. The precursor powders were prepared using several zinc counter ions such as chloride, nitrate and sulphate along with oxalic acid as a precipitating agent. The precursors were decomposed by heating in air resulting in the formation of different shapes of zinc oxide crystals. Variations in ZnO nanostructural shapes were possibly due to the counter ion effect. Sulphate counter ion led to unusual rose-shape morphology. Strong ultrasonic treatment on ZnO rose shows that it was formed by irregular arrangement of micro to nano size hexagonal zinc oxide platelets. The X-ray diffraction studies confirmed the wurzite structure of all zinc oxide samples synthesized using different zinc counter ions. Functional groups of the zinc oxalate precursor and zinc oxide were identified using micro Raman studies. The blue light emission spectra of the various morphologies were recorded using luminescence spectrometer. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Anomalous X-ray scattering study of local structures in the superionic conducting glass (AgBr)0.4 (Ag2O)0.3 (GeO2)0.3

The local structural information in the near-neighbor region of superionic conducting glass (AgBr)0.4(Ag2O)0.3(GeO2)0.3 has been estimated from the anomalous X-ray scattering (AXS) measurements using Ge and Br K absorption edges. The possible atomic arrangements in the near-neighbor region of this glass were obtained by coupling the results with the least-squares variational method so as to reproduce two differential intensity profiles for Ge and Br as well as the ordinary scattering profile. The coordination number of oxygen around Ge is found to be 3.6 at a distance of 0.176 nm, suggesting the GeO4 tetrahedral unit as the probable structural entity in this glass. Moreover, the coordination number of Ag around Br is estimated as 6.3 at a distance of 0.284 nm, suggesting an arrangement similar to that in crystalline AgBr.

Cu(II)-azide polymers with various molar equivalents of blocking diamine ligands: synthesis, structures, magnetic properties with DFT studies

Four new neutral copper-azido polymers [Cu(4)(N(3))(8)(Me-hmpz)(2)](n) (1), [Cu(4)(N(3))(8)(men)(2)](n) (2), [Cu(5)(N(3))(10)(N,N-dmen)(2)](n) (3) and [Cu(5)(N(3))(10)(N,N'-dmen)(5)](n) (4) [Me-hmpz = 1-methylhomopiperazine; men = N-methylethylenediamine; N, N-dmen = N, N-dimethylethylenediamine and N, N'-dmen = N, N'-dimethylethylenediamine] have been synthesized by using various molar equivalents of the chelating diamine ligands with Cu(NO(3))(2)center dot 3H(2)O and an excess of NaN(3). Single-crystal X-ray structures show that the basic asymmetric units of 1 and 2 are very similar, but the overall 1D structures were found to be quite different. Complex 3 with a different composition was found to be 2D in nature, while the 1D complex 4 with 1 : 1 metal to diamine ratio presented several new structural features. Cryomagnetic susceptibility measurements over a wide range of temperature were corroborated with density functional theory calculations (B3LYP functional) performed on the complexes 1-3 to provide a qualitative theoretical interpretation of their overall magnetic behavior.

On the mechanism of plastic flow at 86°k in quenched and aged aluminum

The plastic flow of quenched aluminium at 86°K was investigated by ‘differential-stress’ creep tests in order to evaluate the rate-controlling mechanism in as-quenched and fully aged states. The experimental values of activation volume (4·3 × 10−21 cm3 for as-quenched and 5·5×l0−21cm3 for fully aged) and the total energy for thermal activation process (0·4 ev for both) are in accordance with the jog hardening and loop hardening mechanisms in quenched and fully aged states respectively.

Studies of phosphazenes .11. syntheses and structures of bis(primary amino)hexachlorocyclotetraphosphazenes and their dimethylamino derivatives

The bis(amino)hexachlorocyclotetraphosphazenes, 2-trans-6-N4P4 (NHR)2Cl6, R [dbnd] Me, Pr n Pr i , Bu n , CH2Ph, Ph, are obtained from the reaction of N4P4Cl8 with four mol. equivalents of the appropriate amine. Isomers with 2,4-structures have been isolated for R [dbnd] Bu n , CH2Ph. The 1H and 31P NMR spectra of these bis(amino) compounds and of their dimethylamino derivatives, 2-trans-6-N4P4 (NMe2)6 (NHR)2 are discussed.

Two new 1D chains of Ni(2)Na(2) heterometallic double half-cubane building units: Synthesis, structures and variable temperature magnetic study

An equimolar mixture of Ni(NO(3))(2)center dot 6H(2)O and pyridine-2-aldehyde with two equivalents of NaN(3) in methanol in the presence of NaOMe resulted in the formation of light green precipitate which upon crystallization from dimethylformamide (DMF) yielded light green single crystals [{Ni(2)Na(2)(pic)(4)(N(3))(2)(H(2)O)(2)(MeOH)}center dot MeOH center dot 3H(2)O](n) (1) and [{Ni(2)Na(2)(pic)(4)(N(3))(2)(H(2)O)(4)}center dot 2DMF center dot H(2)O](n) (2) (pic = pyridine-2-carboxylate) at room temperature and high temperature (100 degrees C), respectively. Variable temperature magnetic studies revealed the existence of overall ferromagnetic behaviour with J approximate to + 10 cm(-1) and D approximate to -2 to -7 cm(-1) for 1 and 2, respectively. Negative D values as well as variation of D upon slight distortion of structure by varying reaction temperature were observed. The X-band Electron Paramagnetic Resonance (EPR) spectra of both 2 and 3 were recorded below 50 K. The structural distortion was also implicated from the EPR spectra. Density Functional Theory (DFT) calculations on both complexes were performed in two different ways to corroborate the magnetic results. Considering only Ni(2)(II) dimeric unit, results were J = + 20.65 cm(-1) and D = -3.16 cm(-1) for 1, and J = +24.56 cm(-1) and D = -4.67 cm(-1) for 2. However, considering Ni(2)(II)Na(2)(I) cubane as magnetic core the results were J = +16.35 cm(-1) (1), +19.54 cm(-1) (2); D = -3.05 cm(-1) (1), -4.25 cm(-1) (2).

Injection-molded high-density polyethylene-hydroxyapatite-aluminum oxide hybrid composites for hard-tissue replacement: Mechanical, biological, and protein adsorption behavior

In this article, we report the mechanical and biocompatibility properties of injection-molded high-density polyethylene (HDPE) composites reinforced with 40 wt % ceramic filler [hydroxyapatite (HA) and/or Al2O3] and 2 wt % titanate as a coupling agent. The mechanical property measurements revealed that a combination of a maximum tensile strength of 18.7 MPa and a maximum tensile modulus of about 855 MPa could be achieved with the injection-molded HDPE20 wt % HA20 wt % Al2O3 composites. For the same composite composition, the maximum compression strength was determined to be 71.6 MPa and the compression modulus was about 660 MPa. The fractrography study revealed the uniform distribution of ceramic fillers in the semicrystalline HDPE matrix. The cytocompatibility study with osteoblast-like SaOS2 cells confirmed extensive cell adhesion and proliferation on the injection-molded HDPE20 wt % HA20 wt % Al2O3 composites. The cell viability analysis with the 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay revealed a statistically significant difference between the injection-molded HDPE20 wt % HA20 wt % Al2O3 composites and sintered HA for various culture durations of upto 7 days. The difference in cytocompatibility properties among the biocomposites is explained in terms of the difference in the protein absorption behavior. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Structures of new crystal forms of Mycobacterium tuberculosis peptidyl-tRNA hydrolase and functionally important plasticity of the molecule

The X-ray structures of new crystal forms of peptidyl-tRNA hydrolase from M.similar to tuberculosis reported here and the results of previous X-ray studies of the enzyme from different sources provide a picture of the functionally relevant plasticity of the protein molecule. The new X-ray results confirm the connection deduced previously between the closure of the lid at the peptide-binding site and the opening of the gate that separates the peptide-binding and tRNA-binding sites. The plasticity of the molecule indicated by X-ray structures is in general agreement with that deduced from the available solution NMR results. The correlation between the lid and the gate movements is not, however, observed in the NMR structure.

Polymer based photo detectors

Recent developments in our laboratory related to polymer-based light sensors are reviewed. The inherent processibility of the active polymer medium is utilized in the implementation of different designs for the opto-electronic applications. The utility of these devices as sensitive photodetectors, image sensors and position sensitive detectors is demonstrated. The schottky-type layer formation at interfaces of polymers such as polyalkylthiophenes and aluminum accompanied by the enhanced photo-induced charge separation due to high local electric field is tapped for some of these device structures. The sensitivity of polymer-based field effect transistors to light also provides a convenient lateral geometry for efficient optical-coupling and control of the transistor state. ne range of these polymer-detectors available with the option of operating in the diode and transistor modes should be an attractive feature for many potential applications.

The omega phase formation during laser cladding and remelting of quasicrystal forming AlCuFe on pure aluminum

We report the formation omega phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The omega phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of omega phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as alpha-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that omega phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the omega phase has been suggested.