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

Abstract

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 < , while it decreases with increasing f_NP at 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 and increases with f_NP above , in agreement with the variation of T_g.