Examining Length Scales of Interfacial Dynamics in Ultra-Thin Polymer Glasses

Amorphous polymeric materials are increasingly used in a variety of technologies ranging from organic electronics to gas separation membranes. As many of these applications trend towards the nanoscale, it is imperative to know how the properties of nanoscale polymer glasses compare to those of the bulk material. While many cases have shown that the dynamics of the interfaces affect the properties of a thin film, the length scales of these effects are still heavily debated. In this thesis, I use ellipsometry to perform cooling rate dependent Tg measurements in order to probe the average length scales of interfacial dynamics in ultra-thin polymer glasses. These studies show that segmental motion from the surfaces of a film can influence the dynamics of a material over length scales up to 40 nm, which is over ten times the length scale of segmental motion. Furthermore, they show that while factors such as polymer molecular weight, chain stiffness, and attractive substrate interactions can have an effect on the overall dynamics of the system, they do not change the fact that the dynamics from the air/polymer and polymer/substrate interfaces propagate through the film over long length scales.