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 T-g 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 T-g increased and decreased with increasing NP volume fraction for attractive and repulsive interactions, respectively. The dependence of T-g 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, T-g(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, T-g 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 T-g compared to macroscopic systems.