Measurement of segmental dynamics of polymer glasses in the pre-yield regime

It has been shown that the segmental dynamics of polymer glasses are accelerated by deformation, but little is known quantitatively about the change of dynamics at a small strain. Here, we modify the photobleaching method by performing a deformation within a single optical measurement and measure the segmental dynamics in the pre-yield regime. The results were compared with two sets of theories. One of them is Fluidity model, which assumes that the effect of deformation on the segmental dynamics is controlled by the absolute value of strain rate. Using cyclic deformation protocols, we show that deformations with the same absolute strain rate but different peak strains affect the segmental dynamics differently. The other set are NLE, Eyring and PFVD models, all of which contain explicit relationships between the change of segmental dynamics and the stress. Here, it’s found that the acceleration of the segmental dynamics falls onto a universal curve with respect to peak strains. By comparing the curve with these models, we find that NLE model gives the best fit, which indicates its functional form of the acceleration-stress relationship can describe a polymer glass in the pre-yield regime most closely.