Tunability of the Glass Transition Temperature (T g) of Styrene-based Polymers Confined in Thin Films and Nanospheres

The ability to control and manipulate polymer properties at the nanoscale is of critical importance in designing many technological applications and requires a thorough understanding of the interplay among surfaces, interfaces, and polymer species. While the glass transition temperature (Tg)-confinement effect of polymer thin films has been well documented over the past twenty years, methods for controlling and tuning this effect are still lacking. This thesis presents routes for eliminating, suppressing, and reversing the qualitative direction of the T-confinement effect typically associated with styrene-based polymer films. Additionally, this thesis explores how different confining geometries influence the T-confinement effect.;We demonstrate that the T-confinement behavior of thin polymer films can be suppressed and even eliminated by minute amounts of residual surfactant that remain in the polymer produced from conventional emulsion polymerization. The surfactant is at the free surface layer thereby effectively "capping" the film. We also demonstrate that similar tuning of the T-confinement effect can be achieved through adjusting the fragility parameter of styrene butadiene rubber.;This thesis also presents an approach for reversing the qualitative trend of the T-confinement effect typically seen in polystyrene (PS) films. Similar to hydrogen bonding interactions formed between the ester moiety in poly(methyl methacrylate) films and the oxide layer on silica wafers, pi-pi stacking interactions form between the phenyl moiety in PS and aromatic rings in graphite. Model nanocomposites with PS supported on two graphitic substrates exhibit an enhancement in T as a function of film thickness confinement. This experimental setup affords researchers a physical model and aids in the understanding and designing of carbon-based polymer nanocomposites.;Finally, this work clarifies the controversial nature of the T-confinement effect as it relates to PS particles. The relatively few studies regarding the T-confinement effect for PS nanoparticles have reported conflicting results most likely due to experimental artifacts associated with nanoparticle preparation routes that leave behind small molecules (stabilizers, monomers, etc.). To test this hypothesis, we prepared particles via flash nanoprecipitation and observed an identical T-confinement effect in PS confined to three different geometries.