A systematic study of the relationship between the high-frequency dielectric dissipation factor and water adsorption of polyimide films

Abstract

Low dissipation factor (D_f) at high-frequencies is crucial for the application of dielectric materials in next generation mobile communication. However, the relationship between the high-frequency D_f and the molecular structure remains unclear, and the precision molecular design of high-frequency low D_f materials remains extremely challenging. In this study, seven polyimide films containing different hydrophilic or hydrophobic groups were successfully prepared, and their water adsorption and dielectric properties at high-frequency (10 GHz) were comprehensively studied. By improving the test method of water adsorption, the water adsorption data of PI films were accurately obtained. Both water adsorption and dissipation factor have a good linear relationship with relative humidity, and all correlation coefficients are greater than 0.97. Our results show that the difference in D_f in the as-prepared seven polyimide films is mainly caused by the difference in water adsorption, and in the case of similar water adsorption, the molecular structure of polyimide has little effect on D_f, which has not been explicitly proposed in previous studies. Here, we clearly reveal that water adsorption plays a key role in high-frequency D_f for polyimide films and systematically elucidate the relationship between them, providing theoretical support for the preparation of ultra-low D_f polyimides.