Direct Measurement of Molecular Mobility in Actively Deformed Polymer Glasses
2008; American Association for the Advancement of Science; Volume: 323; Issue: 5911 Linguagem: Inglês
10.1126/science.1165995
ISSN1095-9203
AutoresHau-Nan Lee, Keewook Paeng, Stephen F. Swallen, M. D. Ediger,
Tópico(s)Polymer crystallization and properties
ResumoWhen sufficient force is applied to a glassy polymer, it begins to deform through movement of the polymer chains. We used an optical photobleaching technique to quantitatively measure changes in molecular mobility during the active deformation of a polymer glass [poly(methyl methacrylate)]. Segmental mobility increases by up to a factor of 1000 during uniaxial tensile creep. Although the Eyring model can describe the increase in mobility at low stress, it fails to describe mobility after flow onset. In this regime, mobility is strongly accelerated and the distribution of relaxation times narrows substantially, indicating a more homogeneous ensemble of local environments. At even larger stresses, in the strain-hardening regime, mobility decreases with increasing stress. Consistent with the view that stress-induced mobility allows plastic flow in polymer glasses, we observed a strong correlation between strain rate and segmental mobility during creep.
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