Dynamic Studies of Nano-Confined Polymer Thin Films
This event is part of the PhD Final Oral Exams.
Dissertation Committee: Ophelia K.C. Tsui, Robert Carey, Shyam Erramilli, Karl Ludwig, H.E. Stanley
Previous research found that polymer thin films with thickness in the range of ~1−100 nm often exhibit physical properties different from the bulk counterpart. In order to make the best use of polymer thin films in applications, it is important to understand the physical origins of these deviations. In this talk, I will investigate how different factors influence dynamic properties of polymer thin films upon nanoconfinement, including the glass transition temperature (Tg), effective viscosity (Eta) and self-diffusion coefficient (D). We simultaneously studied the effects of confinement on the Tg, D and Eta of poly(isobutyl methacrylate) films supported by silica (PiBMA/SiOx). Both the Tg and D were found to be independent of film thickness (h0), but Eta was decreased with decreasing h0. Since both D and Eta describe transport phenomena in the films and are known to depend on the same sort of local dynamic properties, it is then a question why D and Eta displayed seemingly inconsistent h0 dependences. We envisage the different h0 dependencies to be caused by Tg, D and Eta being different functions of the local Tg’s (Tg,i) or viscosities, which vary with the film depth. By assuming a three-layer model, we were able to account for the experimental data and resolve this inconsistency. By extending these ideas to the analogous data of polystyrene films supported by silica, we have found a resolution for the long-standing inconsistency regarding the effects of confinement on the dynamics of polymer films.