Accession Number:

ADA222848

Title:

Molecular Dynamics of Physical Aging Processes in Polymer Glasses (Experiment and Theory)

Descriptive Note:

Final rept. 1 Sep 1986-31 Jan 1990,

Corporate Author:

CASE WESTERN RESERVE UNIV CLEVELAND OH

Personal Author(s):

Report Date:

1990-04-16

Pagination or Media Count:

4.0

Abstract:

We have studied free volume and aging in PVAc Polyvinyl Acetate, PMMA Polymethyl Methacrylate, PEMA Polyethylene Methacrylate, and polycarbonates by fluorescence spectroscopy, Electron Spin Resonance ESR, and Positron Annihilation Spectroscopy PAS. The product of the ortho-positronium o-Ps lifetime Tau 3 and its formation probability I3 has a temperature dependence above Tg that follows that of the total free volume. The product I3 Tau 3 shows a significant decrease as a function of time at temperatures below Tg. Some specimens with the same composition and the same free volume yielded different values for the individual factors I3 and Tau 3. This indicates that PAS can distinguish between samples that are indistinguishable by conventional methods. We also obtained preliminary results on simultaneous measurement of the positron lifetime and the momentum of the annihilated positron-electron pair. There is a clear difference between high-momentum and low-momentum lifetime distributions, with a much larger value of I3 for the high momentum curve. This is what one expects from the higher momentum involved in o-Ps annihilation. jg

Subject Categories:

  • Polymer Chemistry
  • Atomic and Molecular Physics and Spectroscopy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE