Effect of the interaction anisotropy of the nanoparticle surface on the glass transition temperature of polymer nanocomposites

The glass transition temperature, Tg, is one of the most significant factors by which the system is characterized because most of the properties of polymer nanocomposites (PNCs) vary considerably below and above the Tg of PNCs. We performed molecular dynamics simulations on PNCs filled with diblock or triblock Janus nanoparticles (JNPs) to investigate the effect of the interaction anisotropy of the NP surface on Tg by comparing with the results of the case of homogeneous nanoparticles (HNPs) with the same averaged polymer-NP coupling strength over the NP surface. The results revealed that the Tg can be shifted to lower values by introducing anisotropy in the surface interactions, in contrast to NPs with isotropic interactions. Moreover, we investigated the contribution of diffusion coefficients of polymer to the Tg. Adding diblock JNPs (DJNPs) enhanced diffusion of polymers when compared with adding HNPs, thereby lowering the Tg. Comparing the diblock and triblock JNP (TJNP) cases, we found that the polymer diffusion of TJNP cases is slower than that of DJNP cases because the TJNPs can make indirect contact via the polymer chains around the entire NP surface.