A simulation study on the effect of nanoparticle size on the glass transition temperature of polymer nanocomposites

The effect of the size of nanoparticles, σ_NP, on the glass transition temperature, T_g, of polymer nanocomposites is studied by using molecular dynamics simulations. The variation of T_g with σ_NP shows two distinct behaviours for polymer nanocomposites at low and high volume fractions of nanoparticles (f_NP). At a low f_NP, T_g decays almost exponentially with σ_NP, whereas at a high f_NPT_g shows a complex behaviour: it initially increases and then decreases with increasing σ_NP. The decrease in T_g with σ_NP is due to the significant decrease of adsorbed polymer monomers, while the increase in T_g with σ_NP is attributed to the slower diffusion of larger nanoparticles. We have also investigated the diffusion and relaxation of polymer chains at a temperature above T_g for both low and high f_NPs. The diffusion constant and relaxation time of polymer chains are highly consistent with the behaviour of T_g.