Anisotropic effects of the glass transition in oriented polyethylene
Abteilung für Experimentelle Physik, Universität Ulm - D-89069 Ulm, Germany
Accepted: 29 May 1998
The influence of orientation on the glass transition of semicrystalline polyethylene was investigated using Brillouin spectroscopy. Orientation was achieved by drawing the sample to 6.55 times its original length. The temperature range covered was 100–300 K. By performing the second logarithmic derivative of the longitudinal sound velocity vs. temperature graph the glass transition is found by a pronounced minimum. In the isotropic sample it takes place at . This curve nearly coincides with that found from longitudinal sound velocity in chain direction of the oriented sample. Perpendicular to the chains no effect shows up. As is discussed, thermal expansion can be ruled out as an explanation of this strong anisotropic effect.
PACS: 64.70.Pf – Glass transitions / 81.05.Kf – Glasses (including metallic glasses) / 78.35.+c – Brillouin and Rayleigh scattering; other light scattering
© EDP Sciences, 1998