STUDIES ON THE DIELECTRIC BEHAVIOUR OF POLYPYRROLE AND ITS COMPOSITES WITH POLY (VINYL CHLORIDE)

Polypyrrole/poly (vinyl chloride) semi-interpenenzrtirtg networks of different compositions are prepared using anunonitun per sulfate initiator at room temperature in pellet.form and lilrrt form and their dielectric properties are studied at different microwave frequencies. An HP 8510 Vector network analyzer interfaced with a computer is used. The cavity-perturbation technique is employed for the study

Swelling behaviour of isora/natural rubber composites in oils used in automobiles

Natural rubber/isora fibre composites were cured at various temperatures. The solvent swelling characteristics of natural rubber composites containing both untreated and alkali treated fibres were investigated in aromatic and aliphatic solvents like toluene, and n-hexane. The diffusion experiments were conducted by the sorption gravimetric method. The restrictions on elastomer swelling exerted by isora fibre as well as the anisotropy of swelling of the composite have been confirmed by this study. Composite cured at 100°C shows the lowest percentage swelling. The uptake of aromatic solvent is higher than that of aliphatic solvent for the composites cured at all temperatures. The effect of fibre loading on the swelling behaviour of the composite was also investigated in oils like petrol, diesel, lubricating oil etc. The % swelling index and swelling coefficient of the composite were found to decrease with increase in fibre loading. This is due to the increased hindrance exerted by the fibres at higher fibre loadings and also due to the good fibre-rubber interactions. Maximum uptake of solvent was observed with petrol followed by diesel and then lubricating oil. The presence of bonding agent in the composites restrict the swelling considerably due to the strong interfacial adhesion. At a fixed fibre loading, the alkali treated fibre composite showed lower percentage swelling compared to the untreated one.

Rheological and Extrudate Behaviour of Natural RubberlLatexReclaim Blends

ABSTRACT: The rheological and extrudate behaviour of natural rubber/latex reclaim blends were evaluated using a capillary viscometer . The study shows that the viscosity of natural rubber decreases marginally on the addition of latex reclaim while the variation of viscosity with shear rate is not affected. The temperature sensitivity of the blends is not affected significantly with the addition of latex reclaim . The extrudates of natural rubber/latex reclaim blends are smooth up to the addition of about 50 wt. percent latex reclaim in filled natural rubber compounds.

Spectral and nonlinear optical characterization of ZnO nanocomposites

The spectral and nonlinear optical characteristics of nano ZnO and its composites are investigated. The fluorescence behaviour of nano colloids of ZnO has been studied as a function of the excitation wavelength and there is a red shift in emission peak with excitation wavelength. Apart from the observation of the reported ultra violet and green emissions, our results reveal that additional blue emissions at 420 nm and 490 nm are developed with increasing particle size. Systematic studies on nano ZnO have indicated the presence of luminescence due to excitonic emissions when excited with 255 nm as well as significant contribution from surface defect states when excited with 325 nm. In the weak confinement regime, the third-order optical susceptibility χ(3) increases with increasing particle size (R) and annealing temperature (T) and a R2 and T2.5 dependence of χ(3) is obtained for nano ZnO. ZnO nanocolloids exhibit induced absorption whereas the self assembled films of ZnO exhibit saturable absorption due to saturation of linear absorption of ZnO defect states and electronic effects. ZnO nanocomposites exhibit negative nonlinear index of refraction which can be attributed to two photon absorption followed by weak free carrier absorption. The increase of the third-order nonlinearity in the composites can be attributed to the enhancement of exciton oscillator strength. The nonlinear response of ZnO nanocomposites is wavelength dependent and switching from induced absorption to saturable absorption has been observed at resonant wavelengths. Such a change-over is related to the interplay of plasmon/exciton band bleach and optical limiting mechanisms. This study is important in identifying the spectral range and the composition over which the nonlinear material acts as an optical limiter. ZnO based nanocomposites are potential materials for enhanced and tunable light emission and for the development of nonlinear optical devices with a relatively small optical limiting threshold.

Luminescence tuning and enhanced nonlinear optical properties of nanocomposites of ZnO–TiO2

In this article we present the spectral and nonlinear optical properties of ZnO–TiO2 nanocomposites prepared by colloidal chemical synthesis. Emission peaks of ZnO–TiO2 nanocomposites change from 340 nm to 385 nm almost in proportion to changes in Eg. The nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behaviour. The nonlinear refractive index and the nonlinear absorption increase with increasing TiO2 volume fraction at 532 nm and can be attributed to the enhancement of exciton oscillator strength. ZnO–TiO2 is a potential nanocomposite material for the tunable light emission and for the development of nonlinear optical devices with a relatively small limiting threshold

The tautomerism, solvatochromism and non-linear optical properties of fluorescent 3-hydroxyquinoxaline-2-carboxalidine-4-aminoantipyrine

The Schiff base, 3-hydroxyquinoxaline-2-carboxalidine-4-aminoantipyrine, was synthesized by the condensation of 3-hydroxyquinoxaline-2-carboxaldehyde with 4-aminoantipyrine. HPLC, FT-IR and NMR spectral data revealed that the compound exists predominantly in the amide tautomeric form and exhibits both absorption and fluorescence solvatochromism, large stokes shift, two electron quasireversible redox behaviour and good thermal stability, with a glass transition temperature of 104oC. The third-order non-linear optical character was studied using open aperture Z-scan methodology employing 7 ns pulses at 532 nm. The third-order non-linear absorption coefficient, b, was 1.48 x 10-6 cm W-1 and the imaginary part of the third-order non-linear optical susceptibility, Im c(3), was 3.36 x10-10 esu. The optical limiting threshold for the compound was found to be 340 MW cm-2.

The tautomerism, solvatochromism and non-linear optical properties of fluorescent 3-hydroxyquinoxaline-2-carboxalidine-4-aminoantipyrine

The Schiff base, 3-hydroxyquinoxaline-2-carboxalidine-4-aminoantipyrine, was synthesized by the condensation of 3-hydroxyquinoxaline-2-carboxaldehyde with 4-aminoantipyrine. HPLC, FT-IR and NMR spectral data revealed that the compound exists predominantly in the amide tautomeric form and exhibits both absorption and fluorescence solvatochromism, large stokes shift, two electron quasireversible redox behaviour and good thermal stability, with a glass transition temperature of 104 oC. The third-order non-linear optical character was studied using open aperture Z-scan methodology employing 7 ns pulses at 532 nm. The third-order non-linear absorption coefficient, b, was 1.48 x 10-6 cm W-1 and the imaginary part of the third-order non-linear optical susceptibility, Im c(3), was 3.36x10-10 esu. The optical limiting threshold for the compound was found to be 340 MW cm-2.

Excitation wavelength dependent fluorescence behaviour of nano colloids of ZnO

In this paper, the fluorescence behaviour of nano colloids of ZnO has been studied as a function of the excitation wavelength. We have found that excitation at the tail of the absorption band gives rise to an emission that shifts with the change of the excitation wavelength. The excitation wavelength dependent shift of the fluorescence maximum is measured to be between 60 and 100 nm. This kind of excitation wavelength dependent fluorescence behaviour, which may appear to be in violation of Kasha’s rule of excitation wavelength independence of the emission spectrum, has been observed for nano ZnO colloids prepared by two different chemical routes and different capping agents. It is shown that the existence of a distribution of energetically different molecules in the ground state coupled with a low rate of the excited state relaxation processes, namely, solvation and energy transfer, are responsible for the excitation wavelength dependent fluorescence behaviour of the systems.

Excitation wavelength dependent fluorescence behaviour of nano colloids of ZnO

In this paper, the fluorescence behaviour of nano colloids of ZnO has been studied as a function of the excitation wavelength. We have found that excitation at the tail of the absorption band gives rise to an emission that shifts with the change of the excitation wavelength. The excitation wavelength dependent shift of the fluorescence maximum is measured to be between 60 and 100 nm. This kind of excitation wavelength dependent fluorescence behaviour, which may appear to be in violation of Kasha’s rule of excitation wavelength independence of the emission spectrum, has been observed for nano ZnO colloids prepared by two different chemical routes and different capping agents. It is shown that the existence of a distribution of energetically different molecules in the ground state coupled with a low rate of the excited state relaxation processes, namely, solvation and energy transfer, are responsible for the excitation wavelength dependent fluorescence behaviour of the systems.

Social Stratification and Consumer Behaviour in Kerala-A Study with Special Reference to Consumer Durables

Department of Applied Economics, Cochin University of Science and Technology

Sorptional Behaviour of Metals on the Sediments and Humic acid of Mangrove Ecosystem

Humic substances are complex polymeric structures.No other polymers with such a wide range of properties are so widely distributed in nature.But still their moleculer structures are unknown. A structural knowledge is essential in determining their reactivity with metals.In the present work structural elucidation of humic acids from three different mangrove ecosystems of Cochin area is done with the available data from functional group analysis and various spectroscopic methods.13C NMR spectra of the solid samples with CPMAS,IR and SEM are very promising in revealing the complex structures of these polymeric substances.Sorptional studies on the sediment and humic acid of mangrove ecosystem reveals that the major portion of the organic matter is not extractable with Sodium hydroxide and humic acid only a small portion of the total organic matter. Humic acid is a good complexing agent and scavenger. Due to the nonextractable nature of the organic matter present with the sediment left after alkali extraction it is a better scavenger.

Weld line behaviour of polymer blends with special reference to PP/HDPE, PP/PS and HDPE/LDPE blends

Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology

A Study on the Engineering Behaviour of Grouted Loose Soils

The constructional activities in the coastal belt of our country often demand deep foundations because of the poor engineering properties and the related problems arising from weak soil at shallow depths.The soil profile in coastal area often consists of very loose sandy soils extending to a depth of 3 to 4 m from the ground level underlain by clayey soils of medium consistency.The very low shearing resistance of the foundation bed causes local as well as punching shear failure.Hence structures built on these soils may suffer from excessive settlements.This type of soil profile is very common in coastal areas of Kerala,especially in Cochin. Further,the high water table and limited depth of the top sandy layer in these areas restrict the depth of foundation thereby further reducing the safe bearing capacity.

Experimental investigation of optical limiting and thermal lensing in toluene solutions of C70

Optical limiting and thermal lensing studies are carried out in C70–toluene solutions. The measurements are performed using 9-ns pulses generated from a frequencydoubled Nd:YAG laser at 532 nm. Optical limiting studies in fullerene molecules lead to the conclusion that reverse saturable absorption is the major mechanism for limiting. Analysis of thermal lensing measurements showed a quadratic dependence of thermal lens signal on incident laser energy, which also supports the view that optical limiting in C70 arises due to sequential two-photon absorption via excited triplet state (reverse saturable absorption).