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Polarized fluorescence spectroscopy is used to investigate the photophysical behavior of poly(p-phenylphenylenevinylene) (PPPV) in polystyrene matrix in comparison with oligomeric model compounds. For this purpose PPPV is modeled by a chain consisting of a distribution of independent oligomeric segments. Excitation energy transfer (EET) between the segments depends on the wavelength of excitation, not only for transfer along an isolated polymer chain, but also for intermolecular transfer at high concentration of PPPV. The spatial range of EET, as indicated by fluorescence depolarization, is reduced for excitation at the long wavelength edge of the absorption spectrum ("red-edge-effect").
Stationary polarized fluorescence spectra of poly(1,4-phenylene-1-phenylvinylene), poly(1,4-phenylene-1,2-diphenylvinylene) and poly[1,4-phenylene-1,2-bis(4-phenoxyphenyl)vinylene] in tetrahydrofuran solution and in polystyrene films were recorded at room temperature. In these matrices, different behaviour is found concerning the Stokes shift, the degree of polarization and the quantum yield; it is interpreted as a viscosity induced effect. The commonly accepted model of a conjugated polymer chain to consist of independent segments of various length should not be applied to the poly(phenylene-arylvinylene)s studied in this work.
A method is developed to determine orientational order parameters <P2> and <P4> of films by steady state fluorescence polarization in a spectrometer with 90° angle between excitation and emission beam. This is the geometry usually found in commercial fluorescence spectrometers. The method includes the determination of the fundamental molecular anisotropy rM of the fluorescent chromophore (doped or intrinsic) in stretched and unstretched films and the determination of instrumental correction coefficients from an isotropic film. As an example, the method is applied to orientation analysis of polyethylene and polystyrene films doped with fluorescent molecules of repetitive styrene units. It is concluded that in uniaxially stretched polyethylene-films orientation of these molecules is dominated by their molecular shape; in polystyrene films orientation is influenced by additional interactions.
For the assessment of the barrier function of the geosphere around a nuclear waste repository information about the nature of the accessible rock pore space and internal surfaces is needed. Intact samples of various types of fresh and altered crystalline rocks have been studied by means of mercury intrusion porosimetry and gas adsorption methods using various adsorbates. Furthermore, fluorescence microscopy and scanning electron microscopy was applied and the results were compared with those of impregnation with carbon-l4-polymethylmethacrylate (PMMA). Additional structural information was derived from hydraulic conductivity determinations using helium gas.
The investigations were focussed on the reliability of these measurements of intact core samples, the influence of rock composition, structure and geological evolution on the microstructure of the matrices and the consequences regarding the retardation properties of the bedrock.
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a useful new technique for the determination of the chemical structure and the molar mass distribution of poly(ethylene oxides). Investigating different alkyloxy and aryloxy polyethylene oxides, we have shown that MALDI-MS gives accurate molar masses, provided that the oligomer masses are above 400 g/mol. Below 400 g/mol, mass discrimination effects have to be taken into account. A perfect fit of MALDI-MS with data, determined independently by supercritical fluid chromatography and high performance liquid chromatography, was obtained.