Glycidyl azide polymer crosslinked through triazoles by click chemistry: curing, mechanical and thermal properties

Glycidyl azide polymer (GAP) was cured through click chemistry by reaction of the azide group with bispropargyl succinate (BPS) through a 1,3-dipolar cycloaddition reaction to form 1,2,3-triazole network. The properties of GAP-based triazole networks are compared with the urethane cured GAP-systems. The glass transition temperature (T-g), tensile strength, and modulus of the system increased with crosslink density, controlled by the azide to propargyl ratio. The triazole incorporation has a higher T-g in comparison to the GAP-urethane system (T-g-20 degrees C) and the networks exhibit biphasic transitions at 61 and 88 degrees C. The triazole curing was studied using Differential Scanning Calorimetry (DSC) and the related kinetic parameters were helpful for predicting the cure profile at a given temperature. Density functional theory (DFT)-based theoretical calculations implied marginal preference for 1,5-addition over 1,4-addition for the cycloaddition between azide and propargyl group. Thermogravimetic analysis (TG) showed better thermal stability for the GAP-triazole and the mechanism of decomposition was elucidated using pyrolysis GC-MS studies. The higher heat of exothermic decomposition of triazole adduct (418kJmol(-1)) against that of azide (317kJmol(-1)) and better mechanical properties of the GAP-triazole renders it a better propellant binder than the GAP-urethane system.

Solvent-induced changes on the polarity of the triplet excited state of 2-chlorothioxanthone: From time-resolved absorption and resonance Raman spectroscopies

Solvent polarity has been known to influence the triplet state structure and reactivity. Here, we present our experimental and theoretical study on the effect of solvent on the lowest triplet excited state structure of 2-chlorothioxanthone (CTX). Time-resolved absorption (TA) spectroscopy has been employed to understand the triplet state electronic structure; whereas solvent-induced structural changes have been studied using time-resolved resonance Raman (TR3) spectroscopy. Both the DFT and TD-DFT calculations have been performed in the solution phase employing self-consistent reaction field implicit solvation model to support the experimental data. It has been observed that CO stretching frequencies of the excited triplet state are sensitive to the solvent polarity and increase with the increase in the solvent polarity. Both TA and TR3 studies reveal that specific solvent effect (H-bonding) is more pronounced in comparison to the nonspecific solvent effect. (C) 2013 Elsevier B.V. All rights reserved.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6-20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS-CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Magnetic and dielectric interactions in nano zinc ferrite powder: Prepared by self-sustainable propellant chemistry technique

The structural, magnetic and dielectric properties of nano zinc ferrite prepared by the propellant chemistry technique are studied. The PXRD measurement at room temperature reveal that the compound is in cubic spinel phase, belong to the space group Fd (3) over barm. The unit cell parameters have been estimated from Rietveld refinement. The calculated force constants from FTIR spectrum corresponding to octahedral and tetrahedral sites at 375 and 542 cm(-1) are 6.61 x 10(2) and 3.77 x 10(2) N m(-1) respectively; these values are slightly higher compared to the other ferrite systems. Magnetic hysteresis and EPR spectra show superparamagnetic property nearly to room temperature due to comparison values between magnetic anisotropy energy and the thermal energy. The calculated values of saturation magnetization, remenant magnetization, coercive field and magnetic moment supports for the existence of multi domain particles in the sample. The temperature dependent magnetic field shows the spin freezing state at 30 K and the blocking temperature at above room temperature. The frequency dependent dielectric interactions show the variation of dielectric constant, dielectric loss and impedance as similar to other ferrite systems. The AC conductivity in the prepared sample is due to the presence of electrons, holes and polarons. The synthesized material is suitable for nano-electronics and biomedical applications. (C) 2014 Elsevier B.V. All rights reserved.

Exclusive ring opening of gem-dihalo-1,2-cyclopropanated oxyglycal to oxepines in AgOAc

Treatment of gem-dihalo-1,2-cyclopropanated D-oxyglycal with primary, secondary, and unsaturated alcohols, in the presence of AgOAc, leads to the formation of chloro-oxepines exclusively. Reaction of the resulting 2-chloro-oxepines with excess alcohol in the presence of AgOAc, do not promote further reactions. This result is in contrast to the reactions of D-glucal derived halo-oxepine with alcohols known previously that lead to the formation of furanoses as the major product under similar reaction conditions. Observation of this study consolidates the reactivity differences of gem-dihalo-1,2-cyclopropanated oxyglycals, as compared to gem-dihalo- 1,2-cyclopropanated glycals. (C) 2014 Elsevier Ltd. All rights reserved.

Titanium nitride thin film anode: chemical and microstructural evaluation during electrochemical studies

TIN thin films with (200) fibre texture are deposited on Cu substrate at room temperature using reactive magnetron sputtering. They exhibit a discharge capacity of 172 mu Ah cm(-2) mu m(-1) (300 mAh g(-1)) in a non-aqueous electrolyte containing a Li salt. There is a graded decrease in discharge capacity when cycled between 0.01 and 3.0 V. Electron microscopy investigations indicate significant changes in surface morphology of the cycled TiN electrodes in comparison with the as deposited TiN films. From XPS depth profile analysis, it is inferred that Li intercalated TIN films consist of lithium compounds, hydroxyl groups, titanium sub oxides and TiN. Lithium diffusivity and reactivity decrease with increase in depth and the major reaction with lithium takes place at film surface and grain boundaries. (C) 2014 Elsevier Ltd. All rights reserved.

C. N. R. Rao and the Growth of Solid State and Materials Chemistry as a Central Domain of Research

In celebrating Professor C. N. R. Rao's 80th birthday, this article recalls his singular contributions to solid state and materials chemistry for about sixty years. In so doing, the article also traces the growth of the field as a central domain of research in chemical sciences from its early origins in Europe. Although Rao's major work lies in solid state and materials chemistry - a field which he started and nurtured in India while its importance was being recognized internationally - his contributions to other areas of chemistry (and physics), viz., molecular spectroscopy, phase transitions, fullerenes, graphene, nanomaterials and multiferroics are equally significant. Illustrative examples of his work devoted to rare earth and transition metal oxides, defects and nonstoichiometry, metal-insulator transitions, investigation of crystal and electronic structures of a variety of solids by means of electron microscopies and photoelectron spectroscopy, superconducting cuprates, magnetoresistive manganites, multiferroic metal oxides of various structures and, last but not the least, development of new strategies for chemical synthesis of a wide variety of solids including nanomaterials and framework solids in different dimensionalities, are highlighted. The article also captures his exemplary role as a science teacher, science educationist and institution builder in post-Independence India.

SELECTIVE ALDEHYDE REDUCTION IN KETOALDEHYDES WITH NaBH4-Na2CO3-H2O AT ROOM TEMPERATURES

A variety of aliphatic and aromatic ketoaldehydes were reduced to the corresponding ketoalcohols with a mixture of sodium borohydride (1.2 equivalents) and sodium carbonate (sixfold molar excess) in water. Reactions were performed at room temperatures over (typically) 2 h, and yields of isolated products generally ranged from 70% to 85%. A biscarbonate-borane complex, (BH3)(2)CO2](2-) 2Na(+), possibly formed from the reagent mixture, is likely the active reductant. The moderated reactivity of this acylborane species would explain the chemoselectivity observed in the reactions. The readily available reagents and the mild aqueous conditions make for ease of operation and environmental compatibility, and make a useful addition to available methodology.

Role of surface chemistry in modulating drug release kinetics in titania nanotubes

Surface chemistry and the intrinsic porous architectures of porous substrates play a major role in the design of drug delivery systems. An interesting example is the drug elution characteristic from hydrothermally synthesised titania nanotubes with tunable surface chemistry. The variation in release rates of Ibuprofen (IBU) is largely influenced by the nature of the functional groups on titania nanotubes and pH of suspending medium. To elucidate the extent of interaction between the encapsulated IBU and the functional groups on titania nanotubes, the release profiles have been modelled with an empirical Hill equation. The analysis aided in establishing a probable mechanism for the release of IBU from the titania nanotubes. The study of controlled drug release from TiO2 has wider implication in the context of biomedical engineering. (C) 2014 Elsevier B.V. All rights reserved.

Determination of Internal Structures of Heterogeneous Nanocrystals Using Variable-Energy Photoemission Spectroscopy

This article describes the determination of the internal structure of heterogeneous nanoparticle systems including inverted core-shell (CdS core and CdSe shell) and alloyed (CdSeS) quantum dots using depth-resolved, variable-energy X-ray photoelectron spectroscopy (XPS). A unique feature of this work is the combination of photoelectron spectroscopy performed at lower X-ray energies (400-700 eV), to achieve surface sensitivity, with bulk sensitive measurements at high photon energies (>2000 eV), thereby providing detailed information about the whole nanoparticle structure with a great accuracy. The use of high photon energies furthermore allows us to investigate nanoparticles much larger than those studied thus far. This capability is a consequence of the much-increased mean free path of the photoelectron achieved at high excitation energies. Our results show that the actual structures of the synthesized nanoparticles are considerably different from the nominal, targeted structures, which can be post facto rationalized in terms of the reactivity of different constituents.

Polymer-grafted multiwall carbon nanotubes functionalized by nitrene chemistry: effect on cooperativity and phase miscibility

The demixing of polystyrene (PS) and poly(vinyl methylether) (PVME) was systematically investigated in the presence of surface functionalized multiwall carbon nanotubes (MWNTs) by melt rheology. As PS-PVME blends are weakly interacting blends, the contribution of conformational entropy increases, resulting in thermo-rheological complexity wherein the concentration fluctuation persists even beyond the critical demixing temperature. These phenomenal changes were followed here in the presence of MWNTs with different surface functional groups. Polystyrene was synthesised by atom transfer radical polymerization and was immobilized onto carboxyl acid functionalized multiwall carbon nanotubes (COOH-MWNTs) via nitrene chemistry in order to improve the phase miscibility in PS-PVME blends. Interestingly, blends with 0.25 wt% polystyrene grafted multiwall carbon nanotubes (PS-g-MWNTs) delayed the spinodal decomposition temperature in the blends by similar to 33 degrees C with respect to both control blends and those with COOH-MWNTs. While the localization of COOH-MWNTs in PVME was explained from a thermodynamic point of view, the localization of PS-g-MWNTs was understood to result from favorable PS-PVME contact and the degree of surface coverage of PS on the surface of MWNTs. The length of the cooperative rearranging region (xi) decreased in presence of PS-g-MWNTs, suggesting confinement effects on large scale motions and enhanced interchain concentration fluctuation.

Sensitivity of meteorological input and soil properties in simulating aerosols (dust, PM10, and BC) using CHIMERE chemistry transport model

The objective of this study is to evaluate the ability of a European chemistry transport model, `CHIMERE' driven by the US meteorological model MM5, in simulating aerosol concentrations dust, PM10 and black carbon (BC)] over the Indian region. An evaluation of a meteorological event (dust storm); impact of change in soil-related parameters and meteorological input grid resolution on these aerosol concentrations has been performed. Dust storm simulation over Indo-Gangetic basin indicates ability of the model to capture dust storm events. Measured (AERONET data) and simulated parameters such as aerosol optical depth (AOD) and Angstrom exponent are used to evaluate the performance of the model to capture the dust storm event. A sensitivity study is performed to investigate the impact of change in soil characteristics (thickness of the soil layer in contact with air, volumetric water, and air content of the soil) and meteorological input grid resolution on the aerosol (dust, PM10, BC) distribution. Results show that soil parameters and meteorological input grid resolution have an important impact on spatial distribution of aerosol (dust, PM10, BC) concentrations.

sigma-Ferrier rearrangement of carbohydrate derived vinylcyclopropanes: a facile approach to oxepane analogs

This article presents our work on the sigma-Ferrier ring-expansion of carbohydrate derived vinylcyclopropanes (VCPs) under electrophilic conditions mediated by chloramine-T and a phase-transfer catalyst. The present work serves as the first example on the studies of the reactivity of carbohydrate VCPs towards the synthesis of densely functionalized oxepane analogues. The work elaborates on a reasonable mechanism for the product formation and our observations on the diastereoselectivity based on control experiments and gas-phase calculations. (C) 2014 Elsevier Ltd. All rights reserved.

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The nonaqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested.

Regioselective Thiolation of Arenes and Heteroarenes: C-H Functionalization Strategy for C-S Bond Formation

A facile transition-metal-free oxidative cross-dehydrogenative coupling reaction involving selective formation of a C-S bond leading to the synthesis of arylthiobenzoxazoles, heteroarylthiobenzoxazoles, and arylthiobenzothiazoles has been described. This highly regioselective C-H functionalization reaction with electron-rich aromatic systems including heteroaromatics is achieved by reversing the reactivity of sulfur in the presence of a suitable oxidant and strong acid.