Physical origin of the second damping peak in ionomers as traced by enthalpy relaxation

Abstract

Ionomers possess two loss factor peaks, thus providing a possibility for the fabrication of novel damping materials. Eisenberg et al. assigned the second damping peak to the glass transition of restricted regions in the ionic cluster. However, the ordinary heat flow curves showed only one glass transition corresponding to the first loss factor peak. Moreover, the conventional view by multiplet/cluster model has been questioned by Simmons due to their different conclusions on the size of restricted regions (Macromolecules 2015, 48, 2313−2323). Meanwhile, we found that the storage modulus of the second damping peak was right in the modulus range of the Rouse relaxation mode. In view of these confusions, enthalpy relaxation characteristics were investigated to clarify the nature of the second loss factor peak. It was found that all the ionomers possessed anomalous enthalpy hysteresis due to the existence of two different but partly coupled glass transitions, while Rouse motion did not cause anomalous enthalpy hysteresis. Furthermore, the heat capacity curves after physical aging clearly showed two glass transition behaviors. These experimental evidences confirmed that the second loss factor peak originated from the glass transition in cluster rather than Rouse relaxation, thus further validating the view by multiplet/cluster model.