Aligned Droplet Patterns by Dewetting of Polymer Bilayers

Dewetting of polymer thin films has been extensively studied in the past two decades as an approach to produce patterned surfaces. Here we report a novel phenomenon where dewetted polymer droplets spontaneously align on a substrate, and the alignment extends over a large scale (millimeters). The patterns are formed by dewetting a bilayer system formed by poly(4-vinylpyridine) (P4VP) thin film (80 nm) on a polystyrene (PS) thin film (100 nm) prepared by spin-coating. We investigated the mechanism of the spontaneous droplet alignment and concluded that the final aligned pattern results from series of aligned defects on the P4VP, which are formed during spin-coating. We identified experimental parameters that control the appearance and the order of the resulting aligned droplets.