R. D. Mathad

High energy electron irradiation effects on polystyrene films

The effect of an 8 MeV electron-beam on the structural, optical and dielectric properties of polystyrene films has been investigated respectively by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–VIS) spectroscopy and electrical impedance (LCR) analysis over a radiation dose in the range of 50–250 kGy using a Microtron accelerator. The FTIR spectral analysis shows no change in the overall structure of the irradiated polystyrene films, except a minor change in the intensity of a few peaks in the FTIR spectrum, indicating that polystyrene is resistant to electron-beam irradiation over the range of radiation doses investigated. The optical band gap analysis using the UV–VIS absorption spectra of the polystyrene shows a small decrease in the optical band gap (E g) and the activation energy with an increase in electron doses. Further, the dielectric measurements over a frequency range of 100 Hz to 1 MHz for the electron-beam-irradiated polystyrene films show that both the dielectric constant and the dielectric loss increase with an increase in electron radiation dose, which may be ascribed to the formation of defect sites in the band gap of polystyrene as a consequence of molecular chain scission in the polymer films upon irradiation.

Electron-beam-induced changes in ultra-high-molecular weight polyethylene

Post-irradiation studies have been carried out to elucidate the effects of electron beam irradiation on the structural, optical, dielectric and thermal properties of ultra-high-molecular weight polyethylene (UHMWPE) films. The modifications in the optical band gap, activation energy, oscillator strength, and transition dipole moment have been investigated as a function of electron radiation dose using UV–Vis absorption spectra of UHMWPE films. The spectral analysis showed a decrease in both the optical band gap and activation energy, whereas the oscillator strength and the transition dipole moment increased with the increase in electron radiation doses. Further, the dielectric measurements indicated a slight increase in the dielectric constant and the ac conductivity of the UHMWPE films upon electron irradiation. The thermal analysis carried out by differential scanning calorimeter and thermo-gravimetric analyzer revealed that the melting temperature, degree of crystallinity and thermal stability of the UHMWPE films increased, obviously, due to the predominant cross-linking following high doses of electron radiation.

Electron-beam irradiation effects on poly(ethylene-co-vinyl acetate) polymer

Poly(ethylene-co-vinyl acetate) (EVA) films were irradiated with a 1.2 MeV electron beam at varied doses over the range 0–270 kGy in order to investigate the modifications induced in its optical, electrical and thermal properties. It was observed that optical band gap and activation energy of EVA films decreased upon electron irradiation, whereas the transition dipole moment, oscillator strength and number of carbon atoms per cluster were found to increase upon irradiation. Further, the dielectric constant, the dielectric loss, and the ac conductivity of EVA films were found to increase with an increase in the dose of electron radiation. The result further showed that the thermal stability of EVA film samples increased upon electron irradiation.

An experimental method of determining the electronic excitation energy migration coefficient in organic liquids

Abstract A method is described for determining the singlet electronic excitation energy migration coefficient in an organic liquid by using the linear behaviour of the rate parameter measured as a function of temperature for a diffusion-controlled bimolecular reaction involving the excited state of the liquid. A value of (5.5±0.5)×10 −5 cm 2 s −1 is reported for the energy migration coefficient of liquid toluene.

On the mechanism of electronic excitation energy migration in organic liquids

Abstract The rate constant for electronic excitation energy transfer from toluene toa fluorescent indole measured as a function of temperature indicates unequivocally that the excitation energy migration is entirely due to resonance interaction and not due to excimer formation-dissociation.

On the mechanism of intermolecular energy transfer encounter in organic liquids

Abstract A study of the electronic energy transfer from toluene to an indole in different types of molecular environments and at various temperatures over the range 293–323 K, suggests unambiguously that the mechanism of the bimolecular energy transfer encounter in liquids is not collisional but essentially involves the long-range coulombic interaction.

A photoabsorption method of measuring molecular diffusion coefficients in liquid mixtures

A photoabsorption technique employing Fick’s law and Beer’s law is described for determining diffusion coefficients of molecules in liquid mixtures. The values for diffusion of toluene, at 323 K, in 1:9 mixtures of toluene–cyclohexane and of toluene–paraffin are found, respectively, to be 1.3 and 0.43×10−5 cm2 s−1. These values are observed to differ significantly from those based on the macroviscosity of the mixtures. Some advantages and limitations of the technique are also considered briefly.

Metal Sorption by Microalgae for Employment in Biotreatment of Environmental Heavy Metal Contamination

The study on the ability of microalgae to accumulate heavy metal pollutants from surrounding environments is important in understanding both the basic mechanism and its application in the biotreatment of heavy metal contamination. The present work reports the results on the biosorption of heavy metals of environmental concern namely chromium, cadmium and lead by the living as well as the nonliving cells of the blue green alga Hapalosiphon stuhlmannii Hieron. and the green alga Scenedesmus quadricauda (Turp.) de Breb. The metal sorption was measured under controlled conditions in which the algal cells were exposed over specified time to different metal concentrations in the range of 0.1–15 .0 µg/ml. The metal sorption by both the living as well as the nonliving algal cells generally increased with the metal concentration and followed the Freundlich isotherm model over the concentration range investigated in the experiments. The sorption capacity for the living as well as the nonliving cells of H. stuhlmannii for the different metals was found to be in the order Pb>Cd>Cr, whereas that for the living cells of S. quadricauda was found to be in the order Pb>Cr>Cd and for the nonliving cells, to be in the order Pb>Cd>Cr. Further the sorption intensity for the living as well as the nonliving cells of H. stuhlmannii for the different metals was found to be in the order Cd>Cr>Pb, whereas that for the living cells of S. quadricauda was found to be in the order Cd>Cr>Pb and for the nonliving cells, to be in the order Cd>Pb>Cr. The variations in the metal sorption by the different algal cells were attributed to the varied physicochemical properties of the cell walls to bind the different metals.

On the role of brownian diffusion in electronic energy transfer between aromatic molecules in liquids

Abstract The rate constant for electronic excitation energy transfer from toluene to a fluorescent indole is determined in viscous paraffin medium over the temperature range 293–353 K (viscosity range 0.047–0.39 P). The results indicate unequivocally that brownian diffusion plays a crucial role in energy transfer in liquid systems.

Effects of dilution, temperature and viscosity on intermolecular energy transfer in scintillators

The efficiency of energy transfer from the first excited electronic singlet state of donor toluene to fluorescent indoles as activators in different types of scintillator systems comprising neat toluene, mixture of toluene and cyclohexane and mixture of toluene and paraffin is determined as a function of temperature in the range 293-353K. The results clearly demonstrate that the dependence of the energy transfer efficiency on dilution, temperature and viscosity is essentially governed by the influence of these factors on the probabilities of decay of excited donor molecules through energy-transfer processes as well as processes involving no energy transfer which exhibit compensatory changes.