Interfacial interaction in polyimide/silica hybrid composites by fluorescence spectroscopy

In this paper, we report that the interfacial interaction in polyimide (PI)/silica hybrid composites can be characterized by a fluorescence spectroscopy. We found that silica shows different effects on the fluorescence behavior of polyimide based on biphenyltetracarboximide (BPDA) depending on the type of diamine, that is, whether it is oxydiphenyldiamine (ODA) or phenylenediamine (PDA). The polyimide/silica hybrid composite films were prepared by thermal imidization and sol-gel method from tetraethoxy silane (TEOS). For the polyamic acid (PAA)/TEOS solutions, the interfacial interaction was discussed in terms of the intermolecular hydrogen bonding between PAA and Si(OH)(4) or complexation between a solvent, N-methylpyrrolidinone (NMP), and PAA. Significant changes in the fluorescence wavelength as well as intensity were observed by the presence of silica particles in the. case of BPDA-PDA/silica composite films as compared to the case of BPDA-ODA/silica composite films. We found that silica has some interaction with BPDA-PDA but no interaction with BPDA-ODA in PI films. The interfacial interaction between silica and BPDA-PDA or BPDA-ODA was explained by different electron-donating strength of the diamines, here, PDA and ODA.