Effects of polymer/filler interactions on glass transition temperatures of filler-filled polymer nanocomposites

We investigated the effects of polymer/filler interactions on the glass transition temperatures Tg of filler-filled polymer nanocomposites. Coarse-grained molecular dynamics simulations of crosslinked polymer networks filled with spherical nanoparticles (NPs) were performed with repulsive, non-attractive, and attractive potentials applied between the NPs and polymers. Only well-dispersed NP-configurations were considered to avoid complicated effects originating from NP aggregation. We confirmed that Tg increased and decreased with increasing NP volume fraction for attractive and repulsive interactions, respectively. The dependence of Tg on the crosslink density was less than that on the NP volume fraction. Moreover, we examined mixed systems with random and artificial assignments of NPs with attractive and repulsive polymer/filler interactions (A-NPs and R-NPs, respectively) in well-dispersed NP configurations. For random assignments with RR-NP = 0.25, 0.5, and 0.75, Tg(RR-NP) was larger than the linear combination of Tg(RR-NP = 0.0) and Tg(RR-NP = 1.0). For the artificial layered NP nanostructures, Tg was smaller than that for the cases with the random assignments. It was concluded that dispersity of A-NPs and R-NPs in nanoscale was an important key to increase Tg compared to macroscopic systems.