Effect of SiO₂ on polymer dynamics in PEO / nanocomposites: A combined experimental and computational approach

The dynamics of polymers in PEO / SiO₂ nanocomposites is investigated experimentally utilizing dielectric relaxation spectroscopy (DS) over a broad range of frequencies and for temperatures both below and above the glass transition temperature, T_g, of the neat polymer. Different compositions were chosen to cover the range from a dilute in nanoparticles (NP) system up to one where the chains are severely confined. The sub-T_g local and the segmental relaxations of the neat PEO are identified in the hybrids, as well. A very weak effect on polymer dynamics is observed in contrast to the effect on PEO conformations or crystallinity observed for these systems. In parallel, atomistic molecular dynamics (MD) simulations have been performed in equivalent systems to predict the polymer dynamic behavior and correlate it to the experimental findings. The segmental relaxation and the center of mass translational dynamics of PEO chains close to the SiO₂ NP are slower compared to the bulk. Moreover, the orientational dynamics of PEO at the PEO/SiO₂ interphase is found to be slower and more heterogeneous (broader distribution of relaxation times) when compared to the bulk one. Similarities and differences between the experimental and theoretical findings are discussed.