Infrared Frequency Shifting in Thermally- and Mechanically-Stressed Polymers (Anharmonicity, Nonequilibrium, Ftir, Fourier, Transform, Spectrometer)

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Metallurgical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Bretzlaff, Robert Stewart

• Engineering, Materials Science

Identifier

(UMI)AAI8422028

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/71808