Curing kinetics of epoxy-anhydride systems using quaternary ammonium guar and hydroxyethyl guar as catalysts

The kinetic parameters for the curing reactions of initially uncured and partly cured samples of the diglycidyl ether of bisphenol-A (DGEBA) with phthalic anhydride and quaternary ammonium compounds of guar gum or quaternary ammonium compounds of hydroxyethyl guar gum as catalyst, with or without n-butanol as diluent, were determined using the differential scanning calorimetry technique with a dynamic scan. To evaluate the kinetic parameters, four different computational methods were applied. The reaction was found to be first-order, with activation energy in the range 65-96 kJ mol^?1.     

Synergistic application of oceanographic variables from multi-satellite sensors for forecasting potential fishing zones: methodology and validation results

This study uses synergistic application of satellite-derived chlorophyll concentration (CC), sea surface temperature (SST) and sea surface wind (SSW) for forecasting potential fishing zones (PFZs). PFZs are validated in near-real time through fishing operations and detailed statistical analysis of fishing operation data. CC and SST images were derived from Indian Remote Sensing Satellite-Ocean Colour Monitor (IRS-OCM) and NOAA-AVHRR, respectively, to delineate the oceanographic features exhibiting different oceanic processes. QuikSCAT/SeaWinds derived sea surface wind vectors were used to understand, quantify and demonstrate the variability of wind-induced water mass flow as well as their impacts on features/oceanographic process. Oceanographic features such as eddies, rings and fronts were found to be shifted according to the speed and direction of the wind. An algorithm was developed to compute water mass transport and feature shift. An improved methodology was developed and demonstrated using these prime variables, which are responsible for fishery resources distribution. PFZ forecasts were generated and validated through near-real-time fishing operations. The fishing operations data were taken from the logbooks of fishing vessels for detailed statistical analysis. On average, 80% of observations were recorded with more yield than monthly mean catch in the respective areas. A paired t-test showed statistically significant results.     

Time dependent piezoresistive behavior of polyvinylidene fluoride/carbon nanotube conductive composite

A piezoresistive nanocomposite was prepared by melt blending multiwall carbon nanotubes (MWCNT) into polyvinylidene fluoride (PVDF). Three time dependencies were examined: quasi-static, transient and cyclic fatigue. The transient response of the strain with time showed viscoelastic behavior that was modeled by the 4-element Burger model. Under quasi-static loading the resistance showed negative pressure coefficient below yield but changed to positive pressure coefficient after yield. The transient time dependence was not observed in the resistance measurements. Under cyclic load, the stress-time and resistance-time were synchronous but the resistance peak value decreased with increasing cycles, which was attributed to charge storage in the nanocomposite.     

Optimization of magnetic arc oscillation process parameters on mechanical properties of AA 5456 Aluminum alloy weldments

The present work pertains to the improvement of mechanical properties of AA 5456 Aluminum alloy welds through magnetic arc oscillation process. Taguchi method was employed to optimize the magnetic arc oscillation welding process parameters of non-heat treatable AA 5456 Aluminum alloy welds for increasing the mechanical properties. The same optimum condition was observed in all the properties. Regression models were developed. The effect of welding current, welding speed, amplitude and frequency on mechanical properties was also studied. Analysis of variance was employed to check the adequacy of the developed models. Microstructures of all the welds were studied and correlated with the mechanical properties.     

Nanostructured porous silicon as functionalized material for biosensor application

In this work by means of PL, FTIR and XPS techniques, state-of-the-art porous silicon (PS) films with good mechanical and optical properties have been effectively utilized for the biofunctionalization purpose for its possible application in immunosensors. The functionalization of the PS surface has been achieved by silanization process using aminopropyltriethoxysilane (APTS) as a precursor. The presence of reactive amino groups on the PS surface along with glutaraldehyde as a linker aids in the covalent binding of the antibody (Human IgG) onto the PS surface. Different antigen concentrations can be detected with a good reproducibility with this technique which opens a huge possibility of using this biofunctionalized material for future biosensors.     

Arrays of carbon nanoflake spherules realised on copper substrate

Arrays of carbon nanoflake spherules (CNSs) have been grown on the copper substrate by the microwave plasma assisted chemical vapour deposition method. Uniform sized CNSs of diameters of 700–950 nm have been produced. The CNSs are free from any other carbon nano-structures. The growth of CNSs has been found to be strongly affected by the undulating surface (crest–trough morphology) of the substrate with preferential growth along the direction of crests. Micro-Raman spectroscopic analysis reveals highly active surface of the graphitic edges of as-grown CNSs. A possible growth mechanism has been proposed which could be used for a large yield of arrays of the CNSs. The field-emission measurements show potential applications of the CNSs in the vacuum electronics devices with a low turn-on field of 7.4 V/μm.     

Nanostructured porous silicon as functionalized material for biosensor application

In this work by means of PL, FTIR and XPS techniques, state-of-the-art porous silicon (PS) films with good mechanical and optical properties have been effectively utilized for the biofunctionalization purpose for its possible application in immunosensors. The functionalization of the PS surface has been achieved by silanization process using aminopropyltriethoxysilane (APTS) as a precursor. The presence of reactive amino groups on the PS surface along with glutaraldehyde as a linker aids in the covalent binding of the antibody (Human IgG) onto the PS surface. Different antigen concentrations can be detected with a good reproducibility with this technique which opens a huge possibility of using this biofunctionalized material for future biosensors.     

Nanocomposites of polypropylene impact copolymer and organoclays: role of compatibilizers

Nanocomposites of polypropylene impact copolymer and organoclays were prepared using different compatibilizers (polypropylene‐graft‐(maleic anhydride) (PPMA), polyethylene‐graft‐(maleic anhydride) (PEMA) and their mixture) and varying percentages of clay (3 and 6%) in an attempt to obtain balanced mechanical properties. The nanocomposites were prepared by melt compounding and test specimens were prepared by injection molding. Mechanical properties such as tensile, flexural and Izod impact strength are reported. The clay dispersion was investigated using wide‐angle X‐ray diffraction while the phase morphology was characterized using scanning electron microscopy. It is shown that the mechanical properties of the system with mixed PPMA and PEMA compatibilizers showed the best balance of mechanical properties among the nanocomposites explored. Copyright © 2006 Society of Chemical Industry     

Introductory to the issue

Introductory to the issue     

Effect of oxidation induced surface state formation on the properties of colloidal CdSe quantum dots

This article addresses on the issue of oxidation on the organically capped CdSe nanoparticles. The surface states properties of the nanoparticles were monitored as a function of time during the natural exposure to oxygen and light, to determine the long term stability of the CdSe quantum dots. CdSe nanoparticles were chemically prepared using three different compositional regimes, viz., Cd rich, Se rich, and stoichiometric and were of different sizes in the range of 5-7 nm. The optical and the structural properties in the three cases were significantly different when the nanoparticles were subjected to natural oxidation. The CdSe nanoparticles were probed using Ar+ ion sputtering used in conjunction with X-Ray Photoelectron Spectroscopy for structural analysis, where as the optical studies were done using UV-VIS and the Photoluminescent measurements. The results showed a blue shift and a considerable decrease in the intensity associated to surface states (lambda approximately 600-700 nm) in case of Se rich case, no shift in stoichiometric CdSe suggesting that its stable against oxidation, and a red shift in PL position in Cd rich regime. The Stoke's shift observed in the nonstoichiometric cases can be associated with the quantum confinement and the stress/strain effects. The result demonstrate the role of Cd/Se stoichiometry in tuning the surface states for tailoring the desired optical properties.