Dipole-relaxation dynamics in a modified polythiourea with high dielectric constant for energy storage applications

Abstract

Enhancing dipole polarization has been demonstrated as an effective approach to increase the dielectric constant of polymer dielectrics and thus to improve their discharged energy density for energy storage applications in electrical power and electronic systems. However, further optimization to get a higher dielectric constant and lower polarization loss hinges upon a more insightful understanding of the dynamics of dipole relaxation. Here, we demonstrate an approach, based on the Dissado-Hill dielectric response model, to probe the dynamics of dipole polarization in an all organic polythiourea (PDTC-HK511) composed of p-phenylene diisothiocyanate (PDTC) as rigid segments and Jeffamine® HK511 as flexible segments. Our results reveal that PDTC-HK511 possesses strong subglass transition β and γ relaxation processes in conjunction with the quasi-DC diffusion process at relatively high temperature and a low frequency range. The γ relaxation enhances the dielectric constant by 20%–25% but causes no apparent loss at the operating temperature and frequency conditions due to the high flexibility and short relaxation time of the dipole orientation. In comparison to β relaxation, the weak interactions and much shorter relaxation time of dipoles in γ relaxation evidenced the large flexibility of dipole movement. This work provides deeper insight into the dipole movement and aids future rational designs of polymers for dielectric energy storage.