Thermodynamic, Raman and electrical switching studies on Si15Te85-xAgx (4 <= x <= 20) glasses

We have investigated thermal properties of bulk Si15Te85-xAgx (4 <= x <= 20) glasses in detail, through alternating differential scanning calorimetry experiments. The composition dependence of thermal parameters reveal the signatures of rigidity percolation and chemical threshold at compositions x = 12 and x = 19, respectively. The stability and glass forming ability of these glasses have also been determined using the data obtained from different thermodynamic quantities and it is found that the Si15Te85-xAgx glasses in the region 12 <= x <= 17 are more stable when compared to other glasses of the same series. Further, the blueshift observed in Raman spectroscopy investigations, in the composition range 12 <= x <= 13, support the occurrence of stiffness threshold in this composition range. All Si15Te85-xAgx (4 <= x <= 20) glasses are found to exhibit memory type switching (for sample thickness 0.25 mm) in the input current range 3-9 mA. The effect of rigidity percolation and chemical thresholds on switching voltages are observed at x = 12 and 19, respectively. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682759]

Friction between a Steel Ball and a Steel Flat Lubricated by MoS2 Particles Suspended in Hexadecane at 150 degrees C

A steel ball was slid on a steel flat lubricated by molybdenum disulfide (MoS2) particles suspended in hexadecane oil at 150 degrees C. The friction data is compared with that obtained when the ball was slid on the flat sprayed apriori with nominally dry MoS2 particles. The friction in the dry experiment was found to increase with temperature while the friction in wet condition was found to decrease with increasing temperature. Micro-Raman and Fourier transform IR spectroscopy are used to explore the roles of environmental moisture and chemical degradation of oil on the formation of antifriction film on the steel substrate.

Electrochemical sensing and photocatalysis using Ag-TiO2 microwires

Anatase Ag-TiO2 microwires with high sensitivity and photocatalytic activity were synthesized via polyol synthesis route followed by a simple surface modification and chemical reduction approach for attachment of silver. The superior performance of the Ag-TiO2 composite microwires is attributed to improved surface reactivity, mass transport and catalytic property as a result of wiring the TiO2 surface with Ag nanoparticles. Compared to the TiO2 microwires, Ag-TiO2 microwires exhibited three times higher sensitivity in the detection of cationic dye such as methylene blue. Photocatalytic degradation efficiency was also found to be significantly enhanced at constant illumination protocols and observation times. The improved performance is attributed to the formation of a Schottky barrier between TiO2 and Ag nanoparticles leading to a fast transport of photogenerated electrons to the Ag nanoparticles.

Spectral moment sum rules for the retarded Green's function and self-energy of the inhomogeneous Bose-Hubbard model in equilibrium and nonequilibrium

We derive exact expressions for the zeroth and the first three spectral moment sum rules for the retarded Green's function and for the zeroth and the first spectral moment sum rules for the retarded self-energy of the inhomogeneous Bose-Hubbard model in nonequilibrium, when the local on-site repulsion and the chemical potential are time-dependent, and in the presence of an external time-dependent electromagnetic field. We also evaluate these expressions for the homogeneous case in equilibrium, where all time dependence and external fields vanish. Unlike similar sum rules for the Fermi-Hubbard model, in the Bose-Hubbard model case, the sum rules often depend on expectation values that cannot be determined simply from parameters in the Hamiltonian like the interaction strength and chemical potential but require knowledge of equal-time many-body expectation values from some other source. We show how one can approximately evaluate these expectation values for the Mott-insulating phase in a systematic strong-coupling expansion in powers of the hopping divided by the interaction. We compare the exact moment relations to the calculated moments of spectral functions determined from a variety of different numerical approximations and use them to benchmark their accuracy. DOI: 10.1103/PhysRevA.87.013628

Characterization and microhardness of Co-W coatings electrodeposited at different pH using gluconate bath: a comparative study

Electrodeposition of Co-W alloy coatings has been carried out with DC and PC using gluconate bath at different pH. These coatings are characterized for their structure, morphology and chemical composition by X-ray diffraction, field emission scanning electron microscopy, differential scanning calorimetry and X-ray photoelectron spectroscopy (XPS). Alloy coatings plated at pH8 are crystalline, whereas coatings electrodeposited at pH5 are nanocrystalline in nature. XPS studies have demonstrated that as-deposited alloy plated at pH8 with DC contain only Co2+ and W6+ species, whereas that alloy plated at pH5 has significant amount of Co-0 and W-0 along with Co2+ and W6+ species. Again, Co2+ and W6+ are main species in all as-deposited PC plated alloys in both pH. Co-0 concentration increases upon successive sputtering of all alloy coatings. In contrast, mainly W6+ species is detected in the following layers of all alloys plated with PC. Alloys plated at pH5 show higher microhardness compared to their pH8 counterparts.

Electromagnetic jigsaw: metal-cutting by combining electromagnetic and mechanical Forces

The magnetic saw effect, induced by the Lorentz force generated due to the application of a series of electromagnetic ( EM) pulses, can be utilized to cut a metallic component containing a pre-existing cut or crack. By combining a mechanical force with the Lorentz force, the cut can be propagated along any arbitrary direction in a controlled fashion, thus producing an `electromagnetic jigsaw', yielding a novel tool-less, free-formed manufacturing process, particularly suitable for hard-to-cut metals. This paper presents validation of the above concept based on a simple analytical model, along with experiments on two materials - Pb foil and steel plate. (C) 2013 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of Professor Bert Lauwers

Preparation of Self Assembled Sodium Oleate Monolayer on Mild Steel and Its Corrosion Inhibition Behavior in Saline water

A self assembled monolayer (SAM) of sodium oleate was generated on mild steel by the dip coating method. Formation of the SAM on mild steel was examined using Infrared Reflection Absorption Spectroscopy (IRRAS) and contact angle measurements. The chemical and anticorrosive properties of the SAM were analyzed using different techniques. IRRAS and water contact angle data revealed the crystallinity and chemical stability of the SAM modified mild steel. The electrochemical measurements showed that the mild steel with the sodium oleate derived SAM exhibited better corrosion resistance in saline water. The effect of temperature and pH on the SAM formation and its anti corrosion ability was explored.

Laser- induced optical properties change in Sb10S40Se50 chalcogenide thin films: An investigation through FTIR and XPS measurements

Chalcogenide glasses are interesting materials for their infrared transmitting properties and photo-induced effects. This paper reports the influence of light on the optical properties of Sb10S40Se50 thin films. The amorphous nature and chemical composition of the deposited film was studied by X-ray diffraction and energy dispersive X-ray analysis (EDAX). The optical constants, i.e., refractive index, extinction coefficient, and optical band gap as well as film thickness are determined from the measured transmission spectra using the Swanepoel method. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The dispersion energy parameter was found to be less for the laser-irradiated film, which indicates the laser-irradiated film is more microstructurally disordered as compared to the as-prepared film. It is observed that laser-irradiation of the films leads to decrease in optical band gap (photo-darkening) while increase in refractive index. The decrease in the optical band gap is explained on the basis of change in nature of films due to chemical disorderness and the increase in refractive index may be due to the densification of films with improved grain structure because of microstructural disorderness in the films. The optical changes are supported by X-ray photoelectron spectroscopy data. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Amide Functionalized Microporous Organic Polymer (Am-MOP) for Selective CO2 Sorption and Catalysis

We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (CONH) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N-2, Ar, and O-2. The CO2 molecule interacts with amide functional groups via Lewis acid base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.

The influence of mesoporous silica in low T-g cyclic olefin copolymer nanocomposite films: Mechanical and moisture barrier studies

In this study, mesoporous silica-cyclic olefin copolymer nanocomposite films were fabricated by solution casting. With an increase in silica loading, the stiffness of the matrix increased. The nanocomposite film shows increased strain to failure with moisture after aging by matrix plasticization. The storage modulus and loss factor for samples with silica content show better results compared with pristine polymer, as indicated by dynamic mechanical analysis. The interaction between filler-polymer chain exhibit hydrophobicity compared to the neat polymer. Water absorption studies at room temperature and near the T-g of the polymer (similar to 64 degrees C) were carried out. The nanocomposites up to 4 wt% filler reduces the water diffusion by forming hydrogen and chemical bonding. The result by calcium degradation test method for moisture permeability and Schottky structured organic device encapsulation under weathering condition confirms the effective reinforcement effect of silica particles in the matrix. (C) 2014 Elsevier Ltd. All rights reserved.

Biofouling and microbially influenced corrosion of stainless steels

Stainless steels are among the most investigated materials on biofouling and microbially-influenced corrosion (MIC). Although, generally corrosion-resistant owing to tenacious and passive surface film due to chromium, stainless steels are susceptible to extensive biofouling in subsoil, fresh water and sea water and chemical process environments. Biofilms influence their corrosion behavior due to corrosion potential ennoblement and sub-surface pitting. Both aerobic and anaerobic microorganisms catalyse microbial corrosion of stainless steels through biotic and abiotic mechanisms. MIC of stainless steels is common adjacent to welds at the heat-affected zone. Both austenite and delta ferrite phases may be susceptible. Even super stainless steels are found to be amenable to biofouling and MIC. Microbiological, electrochemical as well as physicochemical aspects of MIC pertaining to stainless steels in different environments are analyzed.

High-quality ZnO nanorod based flexible devices for electronic and biological applications

Vertically aligned zinc oxide nanorods (ZnO NRs) were synthesized on kapton flexible sheets using a simple and cost-effective three-step process (electrochemical seeding, annealing under ambient conditions, and chemical solution growth). Scanning electron microscopy studies reveal that ZnO NRs grown on seed-layers, developed by electrochemical deposition at a negative potential of 1.5 V over a duration of 2.5 min and annealed at 200 degrees C for 2 h, consist of uniform morphology and good chemical stoichiometry. Transmission electron microscopy analyses show that the as-grown ZnO NRs have single crystalline hexagonal structure with a preferential growth direction of < 001 >. Highly flexible p-n junction diodes fabricated by using p-type conductive polymer exhibited excellent diode characteristics even under the fold state.

Surface modification of textured silicon and its wetting behaviour

Textured silicon (Si) substrate were prepared using various texturing methods both chemical and physical and their water contact angle, surface topography and Raman spectra were studied and investigated. The effect of plasma and chemical treatment on micro/nanostructure and roughness of the surface with and without deposition of Octadecyltrichlorosilane (ODTS, Cl3Si (CH3)(17)), self-assembled monolayer (SAM) is investigated for achieving higher water contact angle (theta(c)). The importance of synergism of texturing with deposition of ODTS SAM in preparing superhydrophobic silicon surfaces has been discussed. It is shown that superhydrophobic silicon surfaces can be achieved on silicon surfaces by coating with ODTS, irrespective of whether it is textured or not, polished or unpolished, provided a chemical treatment is given to the surface prior to the ODTS coating.

Effect of lateral substituent and chain length on mesomorphic properties of novel alkoxy benzyloxy benzoates of cyanophenyl rod-shaped compounds

Three novel homologous series of rod-shaped cyanophenyl alkoxy benzoate liquid crystalline compounds with lateral polar fluorine and chlorine substituent were prepared, and chemical structures of novel materials have been characterized by standard spectral technique and elemental analysis. The mesophase characterization was carried out using the combination of polarized optical microscopy and differential scanning calorimetry. All the compounds exhibit wide thermal range of enantiotropic SmA phase.

Suppression of protein aggregation by gold nanoparticles: a new way to store and transport proteins

Suppression of the aggregation of proteins has tremendous implications in biology and medicine. In the pharmaceuticals industry, aggregation of therapeutically important proteins and peptides while stored, reduces the efficacy and promptness of action leading to, in many instances, intoxication of the patient by the aggregate. Here we report the effect of gold nanoparticles (Au-NPs) in preventing the thermal and chemical aggregation of two unrelated proteins of different size, alcohol dehydrogenase (ADH, 84 kDa) and insulin (6 kDa), respectively, in physiological pH. Our principal observation is that there is a significant reduction (up to 95%) in the extent of aggregation of ADH and insulin in the presence of gold nanoparticles (Au-NPs). Aggregation of these proteins at micromolar concentration is prevented using nanomolar or less amounts of gold nanoparticles which is remarkable since chaperones which prevent such aggregation in vivo are required in micromolar quantity. The prevention of aggregation of these two different proteins under two different denaturing environments has established the role of Au-NPs as a protein aggregation prevention agent. The extent of prevention increases rapidly with the increase in the size of the gold nanoparticles. Protein molecules get physisorbed on the gold nanoparticle surface and thus become inaccessible by the denaturing agent in solution. This adsorption of proteins on AuNPs has been established by a variety of techniques and assays.