Dynamics of polymer films at interfaces and with nano scale fillers

The dynamical properties of Polystyrene (PS) and polymethyl methacrylate (PMMA) thin films are reported. X-ray reflectivity was used to measure the thickness of PS thin films and single wavelength ellipsometry was used to determine the optical refractive index. We found that spin-cast thin films have an anomalous refractive index before annealing. Annealing and cooling down to room temperature do not produce a significant change in density. The refractive index has no significant dependence on molecular weight. Annealing changes the conformation and polarization of polymer chains, and restores the bulk index of refraction.; Transmission Electron Microscope (TEM) micrographs and Atomic Force Microscopy (AFM) indicated that spin casting produces a high degree of exfoliation for Cloisite® 6A clay in PS and PMMA. Yet, absorption measurements find that PMMA is preferentially absorbed over PS to Cloisite® 6A clay. This preferential adsorption causes a decrease in diffusion and an increase of viscosity of PMMA/clay melts. In contrast, no change in either diffusion or rheological response was observed with PS.; Furthermore, we report diffusion coefficient (D₀), measurements for PS or PMMA with colloidal Silica, commercial carbon black (C299), C299 heated to 1100°C, C299 heated to 2400°C, and mixtures of these fillers. We found that, for all polymers, C299 slows the diffusion more than C299-2400, indicating that crystalline structure interacts more weakly than turbostatic structure. PMMA interacts more strongly with C299 than PS. D0 is reduced by up to 50%. AFM shows that carbon clusters are cubic, indicating influence of graphitic crystallites. N299-2400 has slightly larger aggregates.; Finally, in situ neutron reflectivity and SIMS measurements were used to investigate the dynamics of PS thin films in supercritical carbon dioxide (scCO₂). The results show that the large degree of anomalous swelling observed is associated with a decrease in glass transition temperature that occurs only within a narrow region of the phase diagram associated with the density fluctuation ridge in scCO₂ region. Within the ridge the diffusion coefficients scale as M−2 and can be approximated by an effective William-Landel-Ferry (WLF) equation.