Effect of ϒ- irradiation and study of ϒ-induced physico-chemical changes in high performance thermoset obtained by double cycloaddition of munchnone and bis-maleimide

ABSTRACT

Techniques in polymer synthesis are taking different dimensions in the last few decades. Reversible-deactivation radical polymerization processes resulted in a wide range of polymeric architectures made from an almost infinite reservoir of functional building blocks. The concept of click chemistry revolutionized the way how polymer chemists approached synthetic routes. Among the few reactions that could qualify as click approach; the copper-catalyzed azide–alkyne cycloaddition reaction is in the front place. Whether click or not, cycloadditions are powerful tools for designing polymeric materials in a modular fashion, with a high level of functionality and, sometimes responsiveness. Thus we have developed an efficient synthetic platform for the preparation of a new class of polyimide-based high-performance thermosets (HPTs) based on the double 1,3-dipolar cycloaddition of munchnone with bis-maleimides. It is worth mentioning that this report is the first to deal with the changes in physico-chemical properties of HPTs obtained by cycloaddition reaction due to gamma irradiation. The polymers synthesized by this unique technique were irradiated with gamma doses in the range 10–300?kGy. The consequential effect of gamma radiation and the structural modifications induced on HPTs have been studied and discussed as a function of dose using different characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TGA), Field Emission Scanning Electron Microscopy (FESEM) and UV-Vis Spectroscopy.     

Determination of mass attenuation coefficient of low-Z dosimetric materials

The mass attenuation coefficients of some low-Z dosimetric materials with potential applications in dosimetry, medical and radiation protection have been investigated using the Monte Carlo simulation code Monte Carlo N-Particle (MCNP). Appreciable variations are noted for the mass attenuation coefficient by changing the photon energy. The MCNP-simulated parameters are compared with the experimental data wherever possible and theoretical values through the WinXcom program. The simulated results obtained by MCNP generally agree well with the experiment and WinXcom predictions for various low-Z dosimetric and tissue substitute materials. In addition, the mass attenuation coefficients around the k-edges for low-Z dosimetric materials estimated from the MCNP code agree very well with WinXcom prediction. Finally, the results indicate that this simulation process can be followed to determine the interaction parameters of gamma rays in such low-Z materials for which there are no satisfactory experimental values available.     

Orientational Order Parameter in 1-Hexyl-4-(4-Isothiocyanatophenyl) Bicyclo [2,2,2] Octane using X-Rays

Abstract

1-Hexy1-4-(4-isothiocyanatophenyl)bicyclo[2,2,2]octane (HIPBO), a nematic liquid crystal which shows nematic phase in the temperature range 52.8 to 90.2°C, has been used along with imaging plate system to record X-ray Laue type diffraction pattern at different temperatures. For this purpose oriented sample was used. Orientational order parameter was obtained using Fourier method, recently reported by us, and has been compared with that of other existing methods.     

Microrheological studies of regenerated silk fibroin solution by video microscopy

We have carried out studies on the rheological properties of regenerated silk fibroin (RSF) solution using video microscopy. The degummed silk from the Bombyx mori silkworm was used to prepare RSF solution by dissolving it in calcium nitrate tetrahydrate‐methanol solvent. Measurements were carried out by tracking the position of an embedded micron‐sized polystyrene bead within the RSF solution through video imaging. The time dependent mean squared displacement (MSD) of the bead in solution and hence the complex shear modulus of this solution was calculated from the bead's position information. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera at full resolution. By examining the distribution of MSD of beads at different locations within the sample volume, we demonstrate that this probe technique enables us to detect local inhomogeneities at nanometre length scales, not detectable either by a rheometer or from diffusing wave spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2555–2562, 2007     

Stacking faults and microstructural parameters in non-mulberry silk fibres

We have analysed the broadening of X-ray reflections observed in nonmulberry silk fibres in terms of stacking faults and microstructural parameters using a single-order method and have, with these parameters, developed, for the first time, a procedure to compute the whole pattern of these silk fibres. The essential deviations in the values of microstructural parameters obtained from line profile and whole pattern fitting procedures are discussed in this paper.     

Effects of axisymmetric loads on inflated non-linear membranes

This paper describes the effects of various external axisymmetric loads on pressurized hinged spherical membranes taking into account changes in internal pressure, volume, and temperature. “Exact” geometrical non-linearity along with generalized constitutive relations for a highly non-linearly clastic, isotropic, homogeneous, incompressible material are used in the analysis. The specialized case of a Hookean material is also treated.The non-linear equations of membrane equilibrium are derived in terms of additional finite displacements for the case of nonorthogonal curvilinear midsurface coordinates and are then specialized for the problem of an inflated hinged spherical membrane. The resulting two highly non-linear coupled second order differential equations are solved by means of a finite difference and Newton-Raphson iterative procedure. All results are presented in nondimensionalized graphical form.     

Simple,Accurate and Rapid HPTLC Method for Analysis of Theophylline in Post-Mortem Blood and Validation of the Method

JPC – Journal of Planar Chromatography – Modern TLC - Theophylline (1, 3-dimethylxanthine) is used both in the prophylaxis of chronic asthma and chronic obstructive airways disease...     

Simulation of X-ray diffraction patterns for silk fibres using paracrystalline statistics

Using paracrystalline statistics, we have simulated one-dimensional and three-dimensional X-ray diffraction patterns from natural silk fibres for various values of crystal size and lattice distortion parameters. This is in agreement with the experimental observation of X-ray pattern reported earlier.     

Studies on characteristics of lightning generated currents in an interconnected lightning protection system

An in-depth knowledge about the characteristics of lightning generated currents will facilitate evaluation of the interception efficacy of lightning protection systems. In addition, it would aid in extraction of valuable statistics (from measured current data) on local lightning parameters. Incidentally, present day knowledge on characteristics of lightning induced current in typical lightning protection systems is rather limited. This is particularly true with closely interconnected protection systems, like the one employed in Indian Satellite Launch Pad-II. This system is taken as a specific example in the present study. Various aspects suggest that theoretical modelling would be the best possible approach for the intended work. From the survey of pertinent literature, it is concluded that electromagnetic modelling of lightning return-stroke with current source at the channel base is best suited for this study. Numerical electromagnetic code was used for the required electromagnetic field solution and Fourier transform techniques were employed for computing time-domain results. A validation for the numerical modelling is provided by laboratory experiments on a reduced scale model of the system. Apart from ascertaining the influence of various parameters, salient characteristics of tower base currents for different kinds of events are deduced. This knowledge can be used in identifying the type of event, as well as its approximate location. A method for estimation of injected stroke current has also been proposed.