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  • 2000-2004  (1)
  • 1990-1994  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Preparation and spectroscopic characterization of a thin polymer film in ultra high vacuum: 2,5-distyrylpyrazine (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3235-3241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The UHV-preparation and -characterization of thin, highly ordered polymer films of 2,5-distyrylpyrazine is reported. Monomer films were evaporated from a Knudsen cell. Subsequent photo-oligomerization occurs by illumination with UV light. The desorption behavior of the monomers and the lower oligomers was studied by temperature-programmed desorption mass spectrometry (TDS). The photoreaction was monitored in situ by high resolution electron energy loss spectroscopy (HREELS) in the range of electronic transitions. The information obtained from the loss spectra are compared to those from absorption and fluorescence spectroscopy. The results are discussed in the framework of the calculated electronic structure of related compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459793
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic transitions in α-oligothiophene thin films. Comparison of ultraviolet/visible absorption spectroscopy and high resolution electron energy loss spectroscopy investigations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6344-6352 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vapor deposited thin films of a series of α-oligothiophenes are investigated comparatively with polarized ultraviolet/visible absorption spectroscopy (UV/VIS) and by high resolution electron energy loss spectroscopy (HREELS) in specular reflection geometry. The complementary selection rules of these methods allow an assignment of the observed absorption and loss bands according to a Hückel molecular orbital model. By plotting the transition energies of corresponding bands of different members of the homologous series vs the reciprocal of the number of rings, the development of the one-dimensional "π-band-structure'' with an increasing number of rings could be followed. The extrapolation to infinite chain length leads to the electronic properties of an ideal (defect free) polythiophene. Furthermore, characteristic differences were observed in the results obtained from the two methods. The orientation of the molecules in thin films is only detectable with UV/VIS spectroscopy. It is most pronounced for α-quinquethiophene. On the other hand, HREELS gives information about the position of optical parity forbidden electronic transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468458
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Solvation and Solvent Relaxation in Swellable Copolymers as Studied by Time-Resolved Fluorescence Spectroscopy (2000)
    Springer
    Journal of fluorescence 10 (2000), S. 383-392 
    Details
    ISSN: 1573-4994
    Keywords: DANSyl-labeled copolymers ; swelling volume ; time-resolved fluorescence ; solvent relaxation ; rotational depolarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The fluorescent probe dimethylaminonaphthylsulfonamide is covalently bound to the ends of the pol(ethylene glycol) chains of the swellable block copolymers poly(ethylene glycol)–polystyrene (PEG-PS) and poly(ethylene glycol)–poly(ethylene imine) (PEG-PEI) to investigate the molecular mobility inside the polymers, swollen by different liquids. Steady-state and time-resolved studies of the Stokes shift between absorption and fluorescence spectra reveal that the probe is solvated by both the polymer matrix and the liquid phase. The extent of solvation by the liquid and the mobility of the microenvironment of the probe depend on both the swelling volume of the polymer and the solubility of the probe in this liquid. Steady-state and time-resolved fluorescence depolarisation measurements show that the polymer matrix forms a very rigid solvent cage, which almost completely immobilizes the probe. Upon solvation of the probe by the liquid, the mobility of the probe increases. In PEG-PEI swollen by polar solvents, the mobilities of the probe itself and of its microenvironment, although not reaching the values observed in homogeneous solution, are significantly higher than in PEG-PS, due to the hydrophilic nature of the polymeric backbone in PEG-PEI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009482514437
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  • 4
    Electronic Resource
    Electronic Resource
    Application of factor analysis for the interpretation of corrosion results (1992)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 344 (1992), S. 195-198 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Explorative factor analysis is applied to measurements of a chromated aluminium alloy to describe the paint adhesion and corrosion of samples with different coating thickness. Interpretation of various measurements is difficult as the surface behaviour of the material is a superposition of complex interactions. Factor patterns of the measurements describe the independent information contained in the data, the factor scores are used to give an objective classification of the samples. The factor analysis explains the superposition of the protective effect of coating thickness and the destructive effect of defect sites in the coating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00322709
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    Paper (German National Licenses)
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