Deciphering Relaxation Spectra of Amorphous Polymers through Dielectric Spectroscopy of an Epoxy

In contrast to the crystalline solid and gaseous phases, the mechanism behind the behavior of liquids and amorphous solids remains a significant challenge, where current descriptions of relaxation behavior in these materials are highly empirical with tenuous physical significance. Recently, we have found that the dynamic mechanical relaxation behavior of an epoxy resin is better described using a small, finite number of discrete relaxation processes instead of the continuous spectrum of relaxation times that are typically employed. In this work, the broadband dielectric spectroscopy of the same epoxy material is investigated, where isotherms were measured from liquid nitrogen temperatures to well above the glass transition temperature. By comparing the loss spectra between the two techniques, we observe that the same discrete set of relaxation times unifies the description of both mechanical and dielectric data. Each of the discrete relaxation processes exhibits its own temperature dependence that is the same for mechanical and dielectric experiments, although the strength of the individual spectral components is different. The implications of the existence of discrete relaxation spectrum for developing theory of amorphous materials will be discussed.