We have employed novel fluorescence methods in conjuction with ellipsometry and differential scanning calorimetry to characterize the effects of inclusion of well-dispersed silica nanoparticles and carbon nanotubes on the glass transition temperature (Tg) and physical aging behavior of several glass-forming polymers, including polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-vinyl pyridine) (P2VP). In those cases in which nanoparticles are dispersed in polymer without any covalent attachment of polymer to the nanoparticles, three different qualitative results are observed related to Tg. When there are wetted interfaces and the presence of attractive polymer-nanofiller interactions (e.g., hydrogen bonds), the Tg is increased relative to neat, bulk polymer. When there are wetted interfaces but no significant attractive interfacial interactions, the Tg is equal to neat, bulk Tg. When the interface are non-wetted, that is, when a free surface is present between the polymer and the nanofiller, there is a reduction in Tg relative to neat, bulk Tg. These results are well understood by making analogies to studies on confined, ultrathin polymer films. In those cases in which there is covalent bonding between the polymer and the nanofiller, such as in PMMA-decorated single-wall carbon nanotubes (SWCNTs), the type of units involved in the covalent attachment of the polymer to the tubes greatly impacts the extent to the which the Tg of the polymer is increase relative to neat, bulk Tg. For example, major differences in the Tg responses are obseved when ethyl versus dodecyl groups are used as linking units.

Stunning modifications to physical aging are observed when nanofillers possessing either attractive interactions or covalent bonding to the polymer. Physical aging rates as measured by fluorescence and differntial scanning calorimetry exhibit huge reductions relative to those observed in neat, glassy polymer. This suggests that a novel application of polymer nanocomposites made from glass-forming polymer may be related to the production of inherently non-equilibrium materials which have properties that are nearly stable to long-term use in the glassy state.