Interaction of single-walled carbon nanotubes with poly(propyl ether imine) dendrimers

We study the complexation of nontoxic, native poly(propyl ether imine) dendrimers with single-walled carbon nanotubes (SWNTs). The interaction was monitored by measuring the quenching of inherent fluorescence of the dendrimer. The dendrimer-nanotube binding also resulted in the increased electrical resistance of the hole doped SWNT, due to charge-transfer interaction between dendrimer and nanotube. This charge-transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. We also report the effect of acidic and neutral pH conditions on the binding affinities. Experimental studies were supplemented by all atom molecular dynamics simulations to provide a microscopic picture of the dendrimer-nanotube complex. The complexation was achieved through charge transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen, and n-propyl moieties of the dendrimer. (C) 2011 American Institute of Physics. doi:10.1063/1.3561308]

Thermodynamics of water entry in hydrophobic channels of carbon nanotubes

Experiments and computer simulations demonstrate that water spontaneously fills the hydrophobic cavity of a carbon nanotube. To gain a quantitative thermodynamic understanding of this phenomenon, we use the recently developed two phase thermodynamics method to compute translational and rotational entropies of confined water molecules inside single-walled carbon nanotubes and show that the increase in energy of a water molecule inside the nanotube is compensated by the gain in its rotational entropy. The confined water is in equilibrium with the bulk water and the Helmholtz free energy per water molecule of confined water is the same as that in the bulk within the accuracy of the simulation results. A comparison of translational and rotational spectra of water molecules confined in carbon nanotubes with that of bulk water shows significant shifts in the positions of the spectral peaks that are directly related to the tube radius. (C) 2011 American Institute of Physics.

Buckling patterns in diamond-like carbon films

An optical microscopy study of stress relief patterns in diamond-like carbon films is presented. Interesting stress relief patterns are observed which include the well-known sinusoidal type, branching pattern and string-of-beads pattern. The last one is shown to relieve stresses under marginal conditions. Two new stress relief patterns are noted in the present study. One of them is of sinusoidal shape with two extra branches at every peak position. The distribution of different stress relief forms from the outer edge of the films towards the interior is markedly dependent on the film thickness. Our new patterns support the approach in which the stress relief forms have been analysed earlier using the theory of plate buckling.

Functionalised carbon nanotubes from solutions

Refluxing carbon nanotubes in H2SO4-HNO3 results in a clear colourless solution which on removal of the solvent gives a white solid containing functionalised nanotubes; neutralization of the acidic solution results in the precipitation of a brown solid containing nanotubes

Solubilities of Benzene Derivatives in Supercritical Carbon Dioxide

The solubilities of benzene derivatives in supercritical carbon dioxide was determined by the saturation method over the pressure range (9.5 to 14.5) MPa. The solubilities were determined at (308 and 313) K for 1-chloro-2,4-dinitrobenzene and (308, 318, and 328) K for m-dinitrobenzene. At 308K, the solubility (in mole fraction) of 1-chloro-2,4-dinitrobenzene varied from (2.83 to 5.88).10(-3) while the solubility of m-dinitrobenzene increased from (2.05 to 5.54).10(-3) as the pressure increased from (9.5 to 14.5) MPa. However, the solubilities of both compounds decreased with increasing temperature. Models based on the solubility parameter and semiempirical models such as the Mendez-Santiago-Teja model, the Gordillo model, and the association model, were used to correlate the experimental solubility data for the benzene derivatives.

New uniform solid catalyst for the low-temperature oxidation of carbon monoxide: A triple-layered rare earth perovskite containing Co and Cu ions

Oxygen reactivity and catalytic activity of the cobalt-containing layered defect perovskites, YBa2Cu2CoO7+delta and LaBa2Cu2CoO7+delta, in comparison with LaBa2Cu3O7-delta have been investigated employing temperature-programmed desorption (TPD) and temperature-programmed surface reactions (TPSR) in the stoichiometric and catalytic mode using carbon monoxide as a probe molecule. TPD studies showed evidence for the presence of two distinct labile oxygen species, one at (0 0 1/2) sites and the other at (0 1/2 0) sites in LaBa2Cu2CoO7+delta against a single labile species at (0 1/2 0) in the case of two other oxides. The activation energies for the catalytic oxidation of carbon monoxide by oxygen over LaBa2Cu3O7-delta, YBa2Cu2CoO7+delta, and LaBa2Cu2CoO7+delta have been estimated to be 24.2, 15.9, and 13.6 kcal/mol, respectively. The reactivity and catalytic activity of the oxide systems have been interpreted in terms of the structural changes brought about by substituents, guided by a directing effect of the larger rare earth cation. TPSR profiles, structural analysis, and infrared spectroscopic investigations suggest that the oxygen present at (0 0 1/2) sites in the case of LaBa2Cu2CoO7+delta is accessible to catalytic oxidation of CO through a Mars-Van Krevelen pathway. Catalytic conversion of CO to CO2 over LaBa2Cu2CoO7+delta occurs at 200 degrees C. The enhanced reactivity is explained in terms of changes brought about in the coordination polyhedra around transition metals, enhanced basal plane oxygen diffusivity, and redox potentials of the different transition metal cations.

Stereospecific construction of stereogenic vicinal quaternary carbon atoms. Enantiospecific synthesis of (+)-valerane

Stereo- and enantiospecific synthesis of (+)-valerane starting from R-carvone utilising orthoester Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions for the construction of the two vicinal quaternary carbon atoms is described. Copyright (C) 1996 Elsevier Science Ltd.

Stable carbon isotope ratios in Asian elephant collagen: implications for dietary studies

Stable carbon isotope ratios in bone collagen have been used in a variety of dietary studies in modern and fossil animals, including humans. Inherent in the stable isotope technique is the assumption that the isotopic signature is a reflection of the diet and is persistent in collagen because this is a relatively inert protein. Carbon isotope analyses of bones from a southern Indian population of Asian elephant (Elephas maximus), a long-lived mammal that alternates seasonally between a predominantly C3 (browse) and C4 (grass) plant diet, showed two patterns that have important implications for dietary interpretation based on isotopic studies. Relative to the quantity of the two plant types consumed on average, the ?13C signal in collagen indicated that more carbon was incorporated from C3 plants, possibly due to their higher protein contribution. There was a much greater variance in ?13C values of collagen in sub-adult (range -10.5� to-22.7�, variance=14.51) compared to adult animals (range -16.0� to -20.3�, variance=1.85) pointing to high collagen turnover rates and non-persistent isotopic signatures in younger, growing animals. It thus seems important to correct for any significant relative differences in nutritive value of food types and also consider the age of an animal before drawing definite conclusions about its diet from isotope ratios.

Transport properties, structure, and radiation induced defect studies in amorphous carbon films

Amorphous conducting carbon films are prepared by plasma assisted chemical vapour deposition and their d.c. conductivity (similar to 100 Scm(-1)) is studied from 300K down to 4.2K. The films were irradiated by high energy ion beam(I+13, 170 MeV) with a dose of 10(13) ions/cm(2). As a result a marked decrease in conductivity by two to three orders in magnitude was observed. The structural changes and the defects in the films caused by ion irradiation are studied using photoluminescence, persistent photoconductivity, and ESR spectroscopy.

Prediction of nonlocal scaling parameter for armchair and zigzag single-walled carbon nanotubes based on molecular structural mechanics, nonlocal elasticity and wave propagation

Atomic vibration in the Carbon Nanotubes (CNTs) gives rise to non-local interactions. In this paper, an expression for the non-local scaling parameter is derived as a function of the geometric and electronic properties of the rolled graphene sheet in single-walled CNTs. A self-consistent method is developed for the linearization of the problem of ultrasonic wave propagation in CNTs. We show that (i) the general three-dimensional elastic problem leads to a single non-local scaling parameter (e(0)), (ii) e(0) is almost constant irrespective of chirality of CNT in the case of longitudinal wave propagation, (iii) e(0) is a linear function of diameter of CNT for the case of torsional mode of wave propagation, (iv) e(0) in the case of coupled longitudinal-torsional modes of wave propagation, is a function which exponentially converges to that of axial mode at large diameters and to torsional mode at smaller diameters. These results are valid in the long-wavelength limit. (C) 2011 Elsevier Ltd. All rights reserved.

Swing amplification of nonaxisymmetric perturbations in stars and gas in a sheared galactic disk

We present a study of the growth of local, nonaxisymmetric perturbations in gravitationally coupled stars and gas in a differentially rotating galactic disk. The stars and gas are treated as two isothermal fluids of different velocity dispersions, with the stellar velocity dispersion being greater than that for the gas. We examine the physical effects of inclusion of a low-velocity dispersion component (gas) on the growth of non-axisymmetric perturbations in both stars and gas, as done for the axisymmetric case by Jog & Solomon. The amplified perturbations in stars and gas constitute trailing, material, spiral features which may be identified with the local spiral features seen in all spiral galaxies. The formulation of the two-fluid equations closely follows the one-fluid treatment by Goldreich & Lynden-Bell. The local, linearized perturbation equations in the sheared frame are solved to obtain the results for a temporary growth via swing amplification. The problem is formulated in terms of five dimensionless parameters-namely, the Q-factors for stars and gas, respectively; the gas mass fraction; the shearing rate in the galactic disk; and the length scale of perturbation. By using the observed values of these parameters, we obtain the amplifications and the pitch angles for features in stars and gas for dynamically distinct cases, as applicable for different regions of spiral galaxies. A real galaxy consisting of stars and gas may display growth of nonaxisymmetric perturbations even when it is stable against axisymmetric perturbations and/or when either fluid by itself is stable against non-axisymmetric perturbations. Due to its lower velocity dispersion, the gas exhibits a higher amplification than do the stars, and the amplified gas features are slightly more tightly wound than the stellar features. When the gas contribution is high, the stellar amplification and the range of pitch angles over which it can occur are both increased, due to the gravitational coupling between the two fluids. Thus, the two-fluid scheme can explain the origin of the broad spiral arms in the underlying old stellar populations of galaxies, as observed by Schweizer and Elmegreen & Elmegreen. The arms are predicted to be broader in gas-rich galaxies, as is indeed seen for example in M33. In the linear regime studied here, the arm contrast is shown to increase with radius in the inner Galaxy, in agreement with observations of external galaxies by Schweizer. These results follow directly due to the inclusion of gas in the problem.

Preparation and characterization of multiwall carbon nanotube/polypyrrole coaxial fibrils

Multiwall carbon nanotube (MWNT)/polypyrrole (PPy) fibrils were fabricated by template-free in situ electrochemical deposition of PPy over MWNTs, and characterized by electron microscopy and electrical measurements. Scanning and transmission electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length, with the possibility of forming unique Y-junctions. Current (I)-voltage (V) characteristics at various temperatures show nonlinearity due to tunneling and hopping contributions to transport across the barriers. AC conductivity measurements (300-4.2 K) show that the onset frequency scales with temperature, and the nanoscale connectivity in MWNT/PPy fibrils decreases with the lowering of temperature. (C) 2011 Elsevier B.V. All rights reserved.

Experimental results of an activated carbon-HFC 134a adsorption cooling system for thermal management of electronics

Results of performance measurement of a small cooling capacity laboratory model of an adsorption refrigeration system for thermal management of electronics are compiled. This adsorption cooler was built with activated carbon as the adsorbent and HFC 134a as the refrigerant to produce a cooling capacity under 5 W using waste heat up to 90 degrees C. The thermal compression process is obtained from an ensemble of four solid sorption compressors. Parametric study was conducted with cycle times of 16 and 20 min, heat source temperatures from 73 to 87 degrees C and cooling loads from 3 to 4.9W. Overall system performance is analyzed using two indicators, namely, cooling effectiveness and normalized exergetic efficiency. (C) 2011 Elsevier Ltd. All rights reserved.

Oxidation of Sulfur Dioxide in Aqueous Suspensions of Activated Carbon

Sulfur dioxide in aqueous solutions at low pH levels exists both in molecular SO2(aq) and in hydrolyzed ionic form HSO3-. Experiments indicate that only HSO3- is the reacting species in the oxidation catalyzed by activated carbon, while SO2(aq) deactivates by competing with HSO3 for the active sites of the catalyst particles. A mechanism is proposed and a rate model is developed that also accounts for the effect of sulfuric acid (product of the oxidation) on the solubility of sulfur dioxide. It predicts first order in HSO3-, half order in dissolved oxygen, and a linear deactivation effect of SO2(aq), which are confirmed by experimental data. The deactivation reaches a constant level corresponding to saturation of the active sites by SO2(aq). Activation energy for the oxidation is 93.55 kJ mol(-1) and for deactivation is 21.4 kJ mol(-1).