Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

TitleComparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass
Publication TypeJournal Article
Year of Publication2016
AuthorsBending, Benjamin, and M. D. Ediger
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume54
Start Page1957
Date Published06/2016
Abstract

We performed constant strain rate deformation and stress relaxation on a poly(methyl methacrylate) glass at Tg – 19 K, utilizing three strain rates and initiating the stress relaxation over a large range of strain values. Following previous workers, we interpret the initial rate of decay of the stress during the relaxation experiment as a purely mechanical measure of mobility for the system. In our experiments, the mechanical mobility obtained in this manner changes by less than a factor of 3 prior to yield. During these mechanical experiments, we also performed an optical measurement of segmental mobility based on the reorientation of a molecular probe; we observe that the probe mobility increases up to a factor of 100 prior to yield. In the post-yield regime, in contrast, the mobilities determined mechanically and by probe reorientation are quite similar and show a similar dependence on the strain rate. Dynamic heterogeneity is found to initially decrease during constant strain rate deformation and then remain constant in the post-yield regime. These combined observations of mechanical mobility, probe mobility, and dynamic heterogeneity present a challenge for theoretical modeling of polymer glass deformation. 

URLhttp://onlinelibrary.wiley.com/doi/10.1002/polb.24110/full
DOI10.1002/polb.24110