Enhanced Dynamics at the Free Surface of a Molecular Glass Film

Abstract

In this thesis we describe two separate experiments involving the use of gold nanoparticles. The first experiment looks at the use of gold nanoparticles as a localized heat source and the potential application as a cancer treatment. The second experiment, which is the real focus of this thesis, applies gold nanoparticles in the study of the free surface dynamics of glassy thin films.

Gold nanoparticles have the ability to strongly absorb the energy in an incident laser beam and convert that energy into heat. Photothermal therapy is a proposed cancer treatment which exploits this ability to irreparably damage cancerous tissues surrounding gold nanoparticles. In the first chapter of this thesis we explain an experiment designed to probe the local temperatures achieved in such a process. Gold nanoparticles are used to stabilize the boundary of an inverse micelle system which contains an aqueous fluorescent dye solution on it's interior. A temperature dependent fluorescence intensity allows us to probe the temperature changes induced by laser irradiation.

In the remainder of this thesis we describe a separate experiment involving the use of gold nanoparticles to study the free surface dynamics of thin glassy films. There is a growing body of evidence in the literature that thin polymer films in the glassy state exhibit heterogeneous dynamics; specifically that the first few nanometers from an air-polymer interface exhibit enhanced mobility relative to the interior of the film. The underlying mechanism responsible for this enhanced mobility remains elusive, however some believe it to be a direct consequence of the polymeric nature of these films. We describe in detail an experiment aimed at addressing this concern. We deposit gold nanoparticles onto the surface of a molecular (non-polymeric) glassy film and monitor their behaviour upon heating using atomic force microscopy. Our results clearly show the existence of enhanced surface mobility in the system studied and provide strong evidence that enhanced surface mobility should be expected in all glass forming systems.