Nonlinear Dielectric Behavior of Polythiourea under a High Electric Field

Here, we report the nonlinear dielectric behavior of p-phenylene diisothiocyanate-cis-1,4-cyclohexanediamine polythiourea (pPDTC-cCHD-PTU), a kind of polythiourea (PTU) aimed for dielectric energy storage. Broadband dielectric spectroscopy was conducted under various electric fields (0.05-60 kV/mm) to characteristic dielectric permittivity and polarization response of pPDTC-cCHD-PTU. The phenomenon of polarity reversal in the nanoregion was observed by piezoresponse force microscopy (PFM) and related to the enhanced dielectric response at high electric fields. The polarization at low and high electric fields and their underlying mechanisms are found to be significantly different. The dipole polarization is in Langevin saturation when the electric field is less than 20 kV/mm, while the orientational polarization of the polar nanoregion is activated at a higher electric field. The orientational polarization of the polar nanoregion mainly occurs in the frequency range of 2-100 Hz, which significantly increases the permittivity. This work provides a deeper insight of the polarization properties of polythiourea (PTU) under electric fields and aids to rationally design polymers for dielectric energy storage.