| Applying carbon dioxide to polymer processing remains a very attractive and innovative research area, driven by its significant impacts on environmental concerns, scientific and technological advancement.;Advancements in applications are supported by a thorough characterization and fundamental understanding of CO2 interaction with a polymer host.;A novel technique ADSA (Axisymmetric Drop Shape Analysis) is adopted to determine the CO2-induced polymer dilation. The method is shown to be a potent tool to study volumetric property of a gas-pressurized system over a wide range of temperature and pressure. In this study, the dilation isotherms of PMMA and Poly(lactide-co-glycolide) (PLGA) were measured over a wide range of temperature and pressure. In addition, with property estimations from a group contribution method, ADSA can be used to evaluate the characteristic parameters of an equation of state (EOS) by fitting the EOS to measured volumetric data.;The real value of an EOS as a process design tool is the ability to describe all thermodynamic properties, not just those it has been fit to. The experimental swelling data were modeled using the Sanchez-Lacombe equation of state (SLEOS) and the correlated interaction parameter between gas and polymer decreases linearly with the increasing temperature. Then the SLEOS was successfully used to predict the CO2 sorption and Tg depression using the interaction parameter fit by swelling data.;In order to clarify the deviation of the polymer surface T g from its bulk value, and especially the influence of CO 2, an Atomic Force Microscopy (AFM)-based visualization method was developed, in which the gold nanoparticles were deposited onto the surface of a polymer thin film and the embedding profile of those particles was used to probe the surface mobility at annealing conditions.;Finally, efforts toward revealing the underlying mechanism of surface Tg reduction were made. A thermodynamic model that is capable of profiling the mass density near the surface and mapping the entropy distribution was developed by combining gradient theory, the Gibbs-DiMarzio Tg criterion and SLEOS. It clearly shows that, even at temperatures lower than bulk Tg, there is a surface liquid-like layer with reduced density at the scale of 1nm which may serve as the origin of enhanced mobility. (Abstract shortened by UMI.). |
