Negative Thermal Expansion in Ultrathin Plasma Polymerized Films (Postprint)

摘要

Because of the increasing applications of polymer films with nanoscale thickness, it is imperative to fully characterize the physical properties in these films, which could be significantly different from the bulk properties due to the surface and interfacial effects. Interactions with the substrate and high specific surface area (film/air and film/substrate) can cause peculiar properties of the ultrathin polymer films. In a recent study the glass transition of a free standing and supported PS film was found to vary significantly with thickness. Other studies have unveiled several interesting phenomena such as the depth dependent glass transition temperature and thickness dependent thermal expansion. It has been reported that substrate interactions alter the thermal properties of ultrathin poly-(2)-vinylpyridine films. A non monotonic thermal behavior was observed in ultrathin polycarbonate films with a negative and positive thermal expansion below and above glass transition temperature, respectively.