Effect of SiO2 particles on dispersion of montmorillonite (MMT) in polyimide nanocomposite during thermal imidization

In this research, the effect of SiO2 particles on the dispersion behavior of montmorillonite (MMT) in polyimide(4-APS/BTDA)/SiO2–MMT nanocomposite film(where 4-APS is 4-aminophenyl sulfone and BTDA is 3,3′,4,4′-benzophenonetetracarboxylic dianhydride), and the changes in the molecular structure and morphology of the polymer matrix during thermal imidization were characterized by means of temporal analyses. For this purpose, the X-ray diffraction (XRD) patterns of PI/MMT and PI/SiO2–MMT nanocomposite films prepared at different heating steps under ambient atmosphere were studied. The MMT d-spacing in the polymer matrix was determined using Bragg’s equation. The XRD results showed that modified organophilic MMT (OMMT) is initially exfoliated in the poly(amic acid) for both nanocomposite films. The results showed that, with increasing temperature and duration of thermal imidization, the peak of the MMT layers moved to slightly higher angle and also the peak intensity increased concurrently for both nanocomposite films. Comparison of the temporal XRD patterns of PI/MMT and PI/SiO2–MMT nanocomposite films revealed that the increase in the peak intensity as well as the displacement of the peak position of MMT layers were less for the latter film. Indeed, the obtained results indicated that, in the presence of SiO2 particles, there was more dispersion of MMT layers in the polymer matrix. The morphology of all the specimens was investigated by atomic force microscopy. The obtained results showed that presence of SiO2 particles can cause the surface of nanocomposite film to become smoother. The temporal ultraviolet–visible spectra of both nanocomposite films showed a bathochromic shift with increase of the thermal treatment temperature and duration.