Kinetics Model of the Chemical Interactions that Influence the Physical Aging of Polystyrene Nanocomposites

摘要

The enhancement of the physical properties of glassy polymers upon addition of nanoparticles has been extensively studied in the past decade. The chemical origin of the nanoparticles greatly influences the extant of the enhancement suggesting that while the physical interactions between the nanoparticles and the polymer chains have a non-negligible contribution, any chemical interactions that may exist greatly influences the physical properties of the material. This influence results most commonly in modification of the polymer chain mobility and therefore affects the physical aging properties of glassy material. The nature of chemical interactions involved have not been well established, however, based on the electron affinity of some of the most commonly used nanoparticles, we suggest that the interactions occurs as transfer of energy involving excited energy states in the nanoparticles. We attempted to verify and model both qualitatively and quantitatively the nature of these interactions by using molecular probes combined with different nanomaterials and imbedded into thin films of atactic polystyrene. The films were then subjected to thermal treatments and/or irradiated at frequencies that permit excitations of the probe molecules. The physical aging properties of the films were then followed by DSC and FTIR spectra were recorded as a function of temperature to evaluate variations in molecular structure as the amount of nanomaterial was increased. Results indicate that as the nanomaterial reach an excited state, the energy is likely transferred to a neighboring molecule. This may result in intermediate bond formation but can also lead to eventual polymer chain breakage and a reduction of the average molecular weight. A kinetic model of the chemical interactions will also be discussed.