Synthesis and characterization of polyimide/monodispersed colloidal silica hybrid thin films.

In this study, two types of the polyimide-silica hybrid thin films, 6FDA-ODA/SiO2 (FS0-FS50) and PMDA-ODA/SiO2 (PS0-PS40), with different silica content were synthesized by using the sol-gel method. TGA analysis showed that the thermal decomposition temperatures (T(d)) of FS and PS hybrid films were in the range of 457-505 degrees C and 458-516 degrees C, respectively. The T(d) increased with increasing the silica content. The measurement of contact angle and FTIR indicated that the hydrophilic and hydrolytic abilities were significantly improved when the silica content increased. The contact angle of PS0-PS40 films was in the range of 80.3-51.8 degrees. UV-Vis spectra showed that the cutoff wavelength of prepared hybrid films could be tunable through the silica content. The n&k analysis showed that the refractive index (n) of FS and PS hybrid films were in the range of 1.60-1.49 and 1.76-1.59, respectively, which could be controlled by the silica content. The extinction coefficients (k) are almost zero in the wavelength range of 300-900 nm, indicating the prepared hybrid films have an excellent optical transparency in the UV and visible region. TEM images showed that the particle size of silica in the hybrid thin films could be effectively controlled under sufficient content of coupling agent. Moreover, the results of SEM and AFM showed that the ratios of average roughness to thickness for all the prepared hybrid films were under 1.6%. It demonstrated that the prepared polyimide-silica hybrid thin films have an excellent film formability and planarity.