Vibration accordion-like

This has been applied successfully by Mizushima and Shimanouchi and by Shauffele and Shimanouchi to measure the stiffness of polyethylene along the chain. The application of Raman spectroscopy to polymers has been greatly facilitated by the introduction of laser sources. To measure the elastic modulus of a hydrocarbon chain, one must identify the vibration frequencies of the accordion-like motion of the planar zig-zag chain. In order to do this, it is necessary to examine spectra of a... 

Fig. 14. Schematic view of the cross section of polyethylene single crystals. Note that there is an all trans chain segment of a specific length D connected to adjacent segments by chain folding at the surface of the crystal. The chain folds decouple the accordion-like vibrations of the all-trans segment so that the frequency of die vibration of a crystal segment is very close to that of a short chain hydrocarbon of...

If identification of lattice vibrations with those of a continuum is made as in Bom s theory then frequencies even lower than the Raman LA mode would be expected from the extreme anisotropy of the polymer crystal. This may in fact be the case, but to assign continuum properties to the rod used in the accordion mode model is not likely to be... 

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