Feature Size Modulation in Dewetting of Nanoparticle-Containing Ultrathin Polymer Films

Abstract

Ultrathin polymer films (thinner than ∼100 nm) undergo spontaneous rupture on a non-wetting surface with the appearance of random holes due to interfacial van der Waal’s interaction or disjoining pressure. These holes grow in size and coalesce into threadlike morphology, which subsequently disintegrate in an isotropic array of nearly equal-sized droplets, the size (dD) and periodicity (λD) of which scales with the initial film thickness (hF). We show that both λD and dD of the dewetted droplets can be modulated by adding trace amounts of nanoparticles (NPs) in the films. While addition of higher proportion of NPs is known to stabilize the films against dewetting, the presence of a lower amount of NPs leads to non-monotonic variation of λD and dD with hF, with the possible creation of miniaturized dewetted features under certain conditions. We also show that λD and dD of the dewetted films depend on whether dewetting is engendered by thermal annealing of the film beyond the glass transition temperature of the constituent polymer (TG) or by exposing the film to solvent vapor (SV). Our findings reveal that both λD and dD are much larger when the film (both with and without particles) is dewetted in the SV atmosphere, arguably due to penetration of the solvent into the film matrix, resulting in an increase in the effective thickness of the film during dewetting. We show that in SV-mediated dewetting, the much faster dynamics is attributed to solvent penetration through the film and its wetting the substrate, rather than a drastic drop in viscosity. We also observe that SV exposure not only leads to much faster dewetting dynamics, but it also successfully engenders dewetting in films with higher hF, which remain stable when annealed thermally.