Control of Morphology in Pattern Directed Dewetting of a Thin Polymer Bilayer

We report the dewetting of a thin polymer bilayer on a low surface energy topographically patterned substrate with grating geometry. The bilayer, comprising of a polystyrene (PS) top and poly(methyl methacrylate) (PMMA) bottom layer was prepared by direct sequential spin coating on the patterned substrate, using mutually exclusive solvents. Depending on the coating conditions, three distinct initial morphologies of the as coated bilayer is possible: type 1, a discontinuous bottom layer under a discontinuous top layer, resulting in polymer threads confined within the substrate grooves; type 2, discontinuous threads of bottom layer polymer (PMMA) confined within the substrate grooves under a continuous top layer; type 3, continuous bottom and top layers. Our experiments reveal that the initial morphology of the film, particularly, that of the bottom layer significantly influences the final dewetted patterns. For example, in a type 1 or type 2 bilayer the morphology depends significantly on the relative widt...