The viscoelastic properties of polymer thin films can have a significant impact on the performance in many small-scale devices. In this work, we use thermal wrinkling, which is a phenomenon based on a thermally-initiated instability, to measure viscoelastic properties of a polymer thin film as a function of thickness. By monitoring the time-evolved wrinkle wavelength at fixed annealing temperatures, we can infer the stress-relaxation modulus and relaxation time of a polystyrene film as a function of film thickness with the aid of the appropriate buckling mechanics models. Specifically, we are able to identify the rubbery plateau and viscous flow regions as a function of annealing time and temperature above its glass transition. For the polystyrene films investigated, we find that the stress relaxation modulus is thickness-independent for films above 100 nm, while a slight deviation was observed below 100 nm.
Citation: ACS Applied Materials and Interfaces
Pub Type: Journals
polymer, viscoelasticity, thin films, coatings, instabilities, wrinkling