Dynamic Studies of Nano-Confined Polymer Thin Films
This event is part of the Departmental Seminars.
Dissertation Committee: Ophelia K.C. Tsui, Tulika Bose, Shyamsunder Erramilli, Karl Ludwig, Eugene Stanley Abstract: Previous research found that polymer thin films with thickness in the range of ~1−100 nm often exhibit physical properties different from the bulk. Understanding the physical origins of the deviations from bulk-like properties in polymer films under nanoconfinement is of interest for both fundamental research and industrial applications. In this talk, I will discuss how nanoconfinement influences several dynamic properties of polymer thin films, including the glass transition temperature (Tg), effective viscosity (eff) and self-diffusion coefficient (D). First, I will discuss the results obtained from an experiment where I, in collaboration with Ellison’s group in UT Austin, studied the Tg, D and ηeff of poly(isobutyl methacrylate) films supported by silica (PiBMA/SiOx). Both the Tg and D were found to be independent of h0, but eff decreased with decreasing h0. Since both D and ηeff describe transport phenomena known to depend on the local friction coefficient or equivalently the local viscosity, it is then questionable why D and ηeff displayed seemingly inconsistent h0 dependences. We envisage the different h0 dependencies to be caused by Tg, D and ηeff being different functions of the local Tg’s (Tg,i) or viscosities (i), which vary with the film depth. By assuming a three-layer model, we were able to account for the experimental data and resolve the inconsistency. By extending the same ideas to the analogous data of polystyrene films, we found a resolution to the long-standing inconsistency regarding the effects of confinement on the dynamics of polymer films.