Probing Segmental Dynamics of Polymer Glasses during Tensile Deformation with Dielectric Spectroscopy

Abstract

An advanced broadband dielectric relaxation spectroscopy technique was developed to measure dipolar reorientation dynamics in an actively deforming amorphous polymer below the glass transition temperature. The application of a weak oscillating electric field during deformation allows for direct probing chain segment mobility. Results show that the application of a monotonically increasing strain on a glassy poly(vinyl chloride) induces a significant increase of the out-of-phase dielectric permittivity, thereby reflecting enhancement of the transition activity of chain segments. Moreover, the strain-dependent relaxation spectra suggest that the bifurcation of the relaxation processes decreases together with an overall increase in molecular mobility upon active deformation. The dielectric results also display a highly pronounced sensitivity to the apparent strain rate used for the mechanical excitation and isothermal aging prior to the deformation.

Relaxation time of a polymer glass stretched at very large strains

“…The large variation of τ ef f cannot be explained only by the increase of the ∆, but it implies that the stress induces a shift towards high frequencies of the α peak without influencing the high frequency part of the DS. Thus we confirm that the stress accelerates the polymer dynamics as already observed in other experiments [23][24][25][26][27][28], which were limited to the yield points. We have extended the analysis to high values of strain in a polymer which presents stress hardening, finding two very important and unexpected results.…”

“…It is complementary to other techniques, such as Nuclear Magnetic Resonance [23] and the diffusion of probe molecules [24][25][26], used to study the molecular dynamics of polymers under stress. The dielectric spectroscopy has already been used in combination with mechanical deformation to study the dynamics in the amorphous phase of polymer under stress [27,28]. The results of these experiments were limited to the yield point whereas the experimental studies of the microscopic behavior and processes during strain hardening are more scarce.…”

Influence of the amorphous phase molecular mobility on impact and tensile properties of polyamide 6,6

“…On the more fundamental side, the nature of the glass transition in polymers, in relation to the onset of molecular mobility, is still an actively debated subject . Specifically, recent experimental works have shown how the molecular mobility is affected by stress, thus leading to a decrease of T g in the presence of stress . Specifically, the yield stress behavior, characterized by the onset of flow beyond a certain stress level, has been interpreted as due to this plasticization effect (decrease of T g ) under stress.…”

The temperature‐dependent ballistic performance and the ductile‐to‐brittle transition in polymer networks

“…The model argues that as long as sufficient mobility exists within the material, load can be transferred between entanglements, “activating” a larger portion of the network. Similarly, the yielding behavior of polymers is proposed to be related to segmental‐level motions, with an increase in segmental dynamics observed during deformation . Elastic ballistic impact models were used to suggest that the yield stress is related to the ballistic performance .…”