Physics (Internal)

The Effect of Solvent Swelling on the Properties of Polystyrene Thin Films

This event is part of the Preliminary Oral Exam.

Examining Committee:  Ophelia Tsui, Rama Bansil, Edward Kearns, Anatoli Polkovnikov Abstract: Several properties of polymer thin films, including viscosity and glass transition temperature, exhibit deviations from the bulk.  While the thin film behavior is likely due to the increasing importance of both surface effects and confinement of the polymer chains as the film thickness decreases, there is currently no consensus on exactly what is responsible for many experimental observations.  In addition, it has been observed that sample preparation and history can influence certain properties of polymer thin films.  In particular, by spin-coating from solutions of different solvent qualities the resulting films will have different initial chain conformations.  We surmise that upon formation by spin-coating, the chain conformation of a film is still adjustable by means of solvent swelling, resulting in modifications to the amount of entanglement and free volume.  Initial measurements of thermal expansion upon heating after swelling suggest that there is a difference between polystyrene films swelled with a good solvent and a near-theta solvent.  A more detailed investigation studying the effect of swelling on the dewetting behavior of the film indicates that the quality of the solvent affects the characteristic aging time associated with the growth rate of dewetting holes.