Infrared Frequency Shifting in Thermally- and Mechanically-Stressed Polymers (Anharmonicity, Nonequilibrium, Ftir, Fourier, Transform, Spectrometer)
Bretzlaff, Robert Stewart
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https://hdl.handle.net/2142/71808
Description
Title
Infrared Frequency Shifting in Thermally- and Mechanically-Stressed Polymers (Anharmonicity, Nonequilibrium, Ftir, Fourier, Transform, Spectrometer)
Author(s)
Bretzlaff, Robert Stewart
Issue Date
1984
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
Thermal and mechanical stresses alter the spacing of the constituents of a polymer chain, usually resulting in the reduction of the molecular vibration frequency as revealed by the transmission infrared spectroscopy of stressed polymer films. The effect of stress and temperature on infrared frequency shifting and band asymmetry in polymers is investigated experimentally and theoretically. Valence coordinate deformation (molecular strain, or intrachain Gruneisen effect) in individual polypropylene chains accounts for the observed frequency shifting in samples of highly oriented, isotactic polypropylene. Each chain is modelled as a one-dimensional anharmonic system, whose wavefunctions and energies are obtained in the quasiharmonic approximation in order to obtain the stress-induced frequency shifting coefficient (alpha)(,c)(T). Furthermore, we expect that the normalized third derivative (LAMDA) of the carbon-carbon bonding potential will be about the same for any main-chain carbon atoms. Stress-Raman data on oriented polyethylene, analyzed in the skeletal approximation of lumped CH(,2) masses, are consistent with (LAMDA) in a range which brackets the value used by Wool and Boyd for their polypropylene chain analysis.
It is believed that stress-infrared techniques might be used to monitor physical aging in the nonequilibrium glassy state of polymers. The spectra of quenched PVC were subjected to digital subtraction and Fourier self-deconvolution routines to extract the amorphous-state results from competing effects. A slope discontinuity in the skeletal peak frequency versus temperature relation is observed during steady heating, as well as a small frequency shift during isothermal annealing. Theoretical considerations indicate that there are both intra- and inter- molecular contributions to these effects.
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