The significance of dielectric spectroscopy in the study of transition dynamics and morphology of transcrystallinity in polymeric composites

Transcrystallization, characterized by dense nucleation on the fiber surface and constrained radial crystalline growth, results in different crystalline morphology than that of the bulk. Concomitantly, it results in redistribution of the amorphous phase, generating rearrangement of the phase transition pattern. This can be identified by dynamic energy dissipation techniques such as high-sensitivity dielectric spectroscopy performed in this study. Focusing on the glass transition, the dielectric properties of three sets of composites are. considered, namely, aramid fiber-reinforced nylon 66, aramid fiber-reinforced poly(ether ether ketone), and ultrahigh molecular weight fiber-reinforced high-density polyethylene. This study demonstrates that dielectric spectroscopy is a unique experimental tool, highly sensitive to the presence of transcrystallinity via its effect on amorphous phase redistribution. Its sensitivity is reflected by a range of dielectric parameters, namely, the activation energy, the dielectric strength and Kirkwood correlation factor, the loss tangent, and the relaxation peak broadening. A number of composite-dielectric property combinations are presented.