Local orientational mobility of polyimide-based nanocomposites

In the present study, the influence of filler concentration on the dynamic properties of nanocomposites based on the thermoplastic polyimide R-BAPO has been investigated by means of full-atomistic molecular dynamics simulations. The orientational mobility of chain fragments of different lengths has been studied before and after embedding of single-walled carbon nanotubes (SWCNT) into the polymer. Slowing down of the polymer orientational mobility in nanocomposites at temperature T = 600 K above the glass transition temperature has been observed for all considered chain fragments in comparison to unfilled systems. It was found that the relative increase of the rotation relaxation times in the diamine part of R-BAPO in the presence of SWCNT is higher for longer chain fragments. This result is in agreement with recent experimental data and with theoretical predictions for the composites based on homopolymers. On the other hand, the relative change of rotation relaxation times under filler loading in the dianhydride part of R-BAPO demonstrates non-monotonic dependence on the length of chain fragments. This result may be explained by structural inhomogeneity of the dianhydride part. Slowing down of the orientational mobility is accompanied by the increase of the glass transition temperature of the composites on ca. 5–15 K with increase of the nanofiller concentration on ca. 3–6% of mass fraction.