In situ preparation and characterization of polyimide/silica composite hemispheres by inverse aqueous emulsion technique and sol-gel method

Abstract

In this paper, micron-scale polyimide/nano-silica (PI/nano-SiO2) composite hemispheres were fabricated by employing inverse aqueous emulsion technique and sol-gel method. Homogeneous inverse emulsion was obtained through using the precursor solution as dispersed phase which contained poly(amic acid) ammonium salt (PAAS), tetraethyl orthosilicate (TEOS) and deionized water, liquid paraffin (LP) as continuous phase, and Span80 as surfactant. The PI/SiO2 hybrid hemispheres could be got by adding excess dehydrating agent into the emulsion. The Fourier transform infrared (FT-IR) results demonstrated that PAAS had been converted to polyimide (PI) after adding the dehydrating agent into the emulsion and that the success of the reaction between TEOS molecules. The research showed that the morphologies of PI/SiO2 hybrid hemispheres, compared with the pure PI hemispheres, were still hemispherical and did not change with the varied silica contents. The surfaces of these samples were without clear interface between the SiO2 particles and the polymer matrix. And, the SEM images of the hybrid hemispheres after hydrofluoric acid (HF) etching or high temperature calcination showed that the SiO2 particles were well dispersed in the organic component, and the diameter of silica particles was nano-scale. The EDX results of the spheres which were after etching in hydrofluoric acid solution or after calcination showed that some 99.98 % of the silica particles were removed and the success of the removal of the organic component, respectively. Furthermore, thermal gravimetric analysis (TGA) results showed that the thermal stability of PI hemispheres could be improved by incorporating the inorganic component.