Ordered arrays of polymer droplets with triangular, circular, and rod-like shapes

Abstract

We demonstrate that topographically patterned oxide surfaces can direct the dewetting of an overlying polystyrene film and produce triangular, circular, or rod-like droplets. Thin films of polystyrene on oxide surfaces are unstable and will rupture by spinodal dewetting. For our studies, spinodal dewetting is suppressed because the dimensions of oxide patterns are smaller than the dominant instability wavelength. Dewetting is initiated at specific points on the surface by modulating the film curvature, and this drives the formation of unstable polymer rims that break apart into discrete droplets. The symmetry of oxide patterns controls the direction of polymer flow during dewetting, and these dynamics determine the locations and shapes of polymer droplets. Patterns with two-fold symmetry generate drops shaped like rods or bullets, and patterns with three-fold symmetry will produce triangles, distorted circles, or perfect circles.