A strategy for accurate prediction of dielectric permittivity and dielectric strength in polyimide

A strategy was proposed to predict accurately the dielectric permittivity and dielectric strength based on the Onsager local field theory. The molecular dynamic simulation was utilised to analyse the dipole moment fluctuation in polyimide (PI) to reflect the polarisation response of applied electric field. The simulation results revealed that the optical dielectric permittivity and static dielectric permittivity were 2.62 and 3.34, showing that the electronic displacement polarisation of the PI acted as a major contributor. The deviation between simulated and measured values of the frequency-dependent relative dielectric permittivity was no more than 5%, which exhibited high accuracy. As the polarisation response of the polar groups in the PI was at infrared frequencies, the conductive loss may be the dominant role in 102-106 Hz at room temperature. Moreover, the effect of Joule heat on the structure, dielectric permittivity and Young modulus was considered to accurately predict the dielectric strength of the PI (359 kV/mm), which was in agreement with experimental values in the literature. These results establish a clear correlation between structural characteristics and dielectric properties of the PI, which would be the theoretical insights into the design and synthesis of the PI with tailored dielectric properties.