Enhanced dielectric properties of amino-modified-CNT/polyimide composite films with a sandwich structure

Novel amino-modified-CNT/polyimide (NH2-MWNT/PI) flexile composite films with a sandwich structure were prepared through step-by-step casting, in which a dielectric layer (NH2-MWNT/PI composites) intercalated between the two insulating layers (pure PI, acting as both the bottom and the top layers). Due to the high capacitance of the dielectric layer and the effective blocking off conductive paths by the insulating layers, the sandwich composite films show a high dielectric constant and ultralow dielectric loss, and the dielectric constants of the composite films are almost frequency independent between 1 and 1000 kHz. It is notable that the NH2-MWNT/PI ratio of the mid-layer markedly influences the dielectric property of the composite film. When the NH2-MWNT content of the mid-layer is 10 wt%, the multi-layer composite film (P-10-P) shows the highest dielectric constant (ε′) of 31.3 at 1 kHz, while the dielectric loss (tan δ) of the P-10-P is only 0.0016. Furthermore, the obtained multi-layer composite films have high breakdown strength and maximum energy storage density. The mechanical properties and thermal properties of the composite films were also examined in this work.