Observation and Analysis of Molecular Vibration Modes in Polylactide at Terahertz Frequencies

概要

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Terahertz (THz) spectra were obtained for polylactide, and they were analyzed by numerical calculations based on density functional theory. An absorption band was observed at approximately 50 cm-1, which becomes larger when the THz electric field is parallel to the sample drawing direction. An absorption peak with a similar directional dependence appears at approximately 40 cm-1 in the simulation, which is due to normal-mode molecular vibrations parallel to the molecular helix. Since the 50 cm-1 absorption decreases with an increase in crystallinity and the permittivity shows a step-like decrease, the molecular vibrations responsible for the 50 cm-1 band seem to be subjected to strong damping in amorphous regions. On the other hand, another absorption peak at 65 cm-1 with a positive absorption dependence on the sample’s crystallinity is likely to be due to lattice vibration, since it does not appear in the calculations, which only deal with intramolecular vibration.
2010-10-25