Weak non-linearities of amorphous polymer under creep in the vicinity of the glass transition

The creep behavior of an amorphous poly(etherimide) polymer is investigated in the vicinity of its glass transition in a weakly non linear regime where the acceleration of the creep response is driven by local configurational rearrangements. From the time shifts of the creep compliance curves under stresses from 1 to 15 MPa and in the temperature range between \(T_g -10K\) and \(T_g\), where \(T_g\) is the glass transition temperature, we determine a macroscopic acceleration factor. The macroscopic acceleration is shown to vary as \(e^{-(\Sigma /Y)}\) temperature with \(n=2 \pm 0.2\), where \(\Sigma \) is the macroscopic stress and Y is a decreasing function of compliance. Because at the beginning of creep, the stress is homogeneous, the macroscopic acceleration is thus similar to the local one, in agreement with the recent theory of Long et al. (Phys Rev Mat 2:105601, 2018) which predicts \(n=2\). For larger compliances, the decrease of Y is interpreted as a signature of the development of stress disorder during creep.

Left: The acceleration of creep kinetics in a weakly non-linear regime in the vicinity of the glass transition is described through an acceleration function F which depends on both the applied stress and the compliance J(t) as a result of the stress induced shift of the relaxation time of nanometric domains (from top to bottom: increasing applied creep stresses). Right : Description of an amorphous polymer glass as a disordered medium made up of nanometric domains with widely distributed relaxation times.