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

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 upon 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 upon 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.

32 pages, 47 references, 10 figures

References in corpus (1)

• Three-dimensional imaging of colloidal glasses under steady shear

Cited by in corpus (4)

• Reversing strain deformations probe mechanisms for enhanced segmental mobility of polymer glasses
• Molecular rotors to probe the local viscosity of a polymer glass
• Rejuvenation versus overaging: The effect of cyclic loading/unloading on the segmental dynamics of PMMA glasses
• Thermalized formulation of soft glassy rheology