Using torsional dilatometry to measure the effects of deformations on physical aging

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Conference Proceeding

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The physical aging of polymer glasses, a phenomenon not completely understood, is an important fundamental topic to the polymer physicist as well as an area of practical concern, since the long-time performance of composites relies on the properties of the matrix, many of which are polymer glasses. Here we present results from our study of an epoxy network (Jeffamine D400/DGEBA, described previously), employing torsional dilatometry to simultaneously measure volume changes and torque relaxation from strains imposed after a quench from 44 to 33.5 C (Tg = 42.4 C). To summarize, in concurrence with the speculations of Struik, we measure volume increases induced by torsion during the slow aging contraction from the quench. The torque relaxation data superpose, but must be shifted farther for tests at 1% strain than those at 3% strain. This does not, however, indicate an erasure of aging on the molecular level, since there is no difference between the ultimate equilibration times based on the evolution of the torque relaxation, in agreement with Lee's data. Further, the sample contraction from the quench is unaltered by subsequent torsional deformations, though these momentarily increase sample volume. The dilatation induced from the torsion relaxes much more rapidly than the slow contraction from the quench. In fact, the equilibration time for volume recovery from the later also exceeds the equilibration time for torque relaxations by at least an order of magnitude, suggesting that the mechanical properties and volume changes are affected differently by physical aging.

Publication Source (Journal or Book title)

American Chemical Society, Polymer Preprints, Division of Polymer Chemistry

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