Photoluminescence, thermal and surface properties of triarylimidazole-containing polyimide nanocomposite films

In this work, a triarylimidazole-containing diamine 2-(4-methylphenyl)-4,5-bis(4-(4-amino-2-trifluoromethylphenoxy)phenyl)imidazole (MPBAI) was firstly synthesized and polymerized with 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) to prepare transparent polyimide (PI) films by means of thermal imidization. Then, inorganic nanoparticles including silica (SiO₂), alumina (Al₂O₃) and silicon nitride (Si₃N₄) were separately introduced into the PI(MPBAI-CBDA) with different mass fractions of 0.02%, 0.10%, 0.50% and 2.50% to obtain three series of PI nanocomposite films. All these films were close to colorless and transparent, although the light transmittance showed a downward trend due to the introduction of nanoparticles. Moreover, as the content of inorganic nanoparticles increased, the fluorescence intensities of these films were increased. Comparatively, the improvement effect of nano-SiO₂ was the most obvious. When the content of SiO₂ was 2.50%, the maximum intensity of the fluorescence absorption peak was increased by 9.6 times, and the absolute fluorescence quantum yield reached 17.2%, about 5.2 times that of the original PI film. Moreover, the maximum absorption peak produced a red shift of 85 nm due to the addition of 2.50% Si₃N₄, which was probably caused by the weakening of fluorescence quenching effect and high permittivity. The nanocomposites exhibited high glass transition temperatures of around 300 °C and excellent thermal stabilities. The surface hydrophobicity was changed by adjusting the mass and type of nanoparticles. Thus, this work provided a simple way to improve the photoluminescence effect by introducing the nanoparticles. The functional films will be expected to be applied in some optical applications.