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

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