| Optical measurement of dye reorientation has been used to investigate deformation-induced segmental mobility in polymer glasses. This information is critical for understanding the deformation behavior of glassy polymers and for testing existing models of polymer glass deformation. In an experiment on a PMMA glass, up to 2000-fold increases in mobility are observed during tensile creep deformation, supporting the view that enhanced segmental mobility allows flow. While the Eyring model describes this mobility enhancement well in the pre-flow regime, it fails to capture the larger mobility enhancement after flow onset. In this regime, the distribution of relaxation times narrows significantly, indicating a more homogenous ensemble of local environments. Regions of lower mobility accelerate their dynamics more in response to an external stress than do regions of high mobility, thus local environments in the sample become more dynamically homogeneous during flow. |
