A novel shift in the glass transition temperature of polymer nanocomposites: a molecular dynamics simulation study

The effect of the loading of nanoparticles on the glass transition temperature, T-g, of polymer nanocomposites is studied by using molecular dynamics simulations. T-g is estimated from the variation of system volume with temperature and the temperature-dependent diffusion of the polymer described by the Vogel-Fulcher-Tammann law. The estimated values of T-g from the two methods are consistent with each other. Results show that T-g can be regulated by changing the volume fraction of nanoparticles, f(NP). A novel shift in T-g is observed, that is, T-g increases with f(NP) at f(NP) < f(NP)*, while it decreases with increasing f(NP) at f(NP) > f(NP)*. The basic mechanism behind the novel shift in T-g is the competition between the attraction of nanoparticles towards polymer chains and the fast diffusion of nanoparticles. The increase in T-g at low f(NP) is due to the attraction of nanoparticles, whereas the decrease in T-g at high f(NP) is attributed to the fast diffusion of nanoparticles. The diffusion of the polymer above T-g is also investigated. The diffusion of the polymer decreases with increasing f(NP) below f(NP)* and increases with f(NP) above f(NP)*, in agreement with the variation of T-g.

Automated summary

The loading of nanoparticles has a significant impact on the glass transition temperature of polymer nanocomposites. The changes in T-g with varying volume fractions of nanoparticles reveal a novel shift, indicating a competition between nanoparticle attraction and fast diffusion in regulating T-g. Additionally, the diffusion of the polymer above T-g also shows a similar trend with the variation of T-g with nanoparticle volume fraction.