*Effect of Molecular Structure Modification and Nano-Doping on Charge Transportation… DOI: http://dx.doi.org/10.5772/intechopen.92024*

200°C (1 h), 250°C (1 h) and 300°C (1 h). After the heating was stopped, waited for 6 hours, and the PI film with a certain thickness was prepared.

In addition, the nano-composite polyimide film was prepared by in-situ polymerization. Firstly, the nano-particles Al2O3 (particle size is less than 20 nm) and surface modifier KH550 were placed in an organic solvent DMAc for ultrasonic process for 1 hour to ensure that the nanoparticles are uniformly dispersed in the organic solvent. Then the appropriate amount of ODA was added into solution and stir for 1 hour. The PMDA was added to the suspension in batches under the water bath environment at a constant temperature of 40°C, and mechanical stirring was continued until the viscosity of the entire reaction solution suddenly increased. After degassing and imidization, PI films doping with different contents of Al2O3 (0, 1, 3, 5, 7 wt%) with a certain thickness were obtained. The scanning electron microscope (SEM) was used to observe the presence of nanoparticles in distribution in the PI matrix.

The surface molecular modification is achieved in terms of surface fluorination. The PI sample is placed in a closed reactor, the air inside the reactor is purged, and the reactor is filled with a certain proportion of fluorine gas and nitrogen gas mixture (12.5 and 20%). The internal reaction temperature was adjusted by the temperature control device (reaction temperature is room temperature and 55°C, respectively), the air pressure was 500 mbar, and the reaction time was 15, 30, 45, and 60 min. The sample after surface molecular modification was used to study the effect of different reaction time on the surface and space charge of the PI sample. The SEM and infrared spectrum analysis tester were used to verify the effect of fluorination.

The multilayer PI sample is a composite of pure single-layer PI film with the same fluorination time.
