The glass-rubber and sub-glass relaxation characteristics of model polymer nanocomposites have been investigated via dynamic mechanical and dielectric methods. Two series of nanocomposites were studied; (i) rubbery nanocomposites prepared via UV photopolymerization of poly(ethylene glycol) diacrylate [PEGDA] in the presence of MgO or SiO2 nanoparticles, and (ii) glassy nanocomposites prepared via solution casting of polyetherimide [Ultem PEI] in combination with either native SiO2, or surface-modified (i.e., hydrophobic) silica particles. Both systems are of interest owing to their potential for use as gas separation membranes.

Dynamic mechanical and dielectric measurements revealed offsets in the position of the glass-rubber relaxation in the nanocomposites as compared to the unfilled polymer that reflect the character of the particle-polymer interaction as well as possible physical confinement. Depending upon the specific nanocomposite system, both an upward shift in the bulk Tg, as well as the emergence of a second segmental relaxation event at higher temperature were detected. These phenomena, as well as potential sub-glass perturbations, are examined as a function of particle loading, particle surface chemistry and nanocomposite morphology.