Macrophase Separation of Block Copolymer Blends in Thin Films

The behavior of macrophase-separating blends of symmetric polystyrene-b-poly(methyl methacrylate) block copolymers in thin films on non-preferential surfaces was characterized with respect to the blends' molecular weights and composition. When the molecular weight ratio of block copolymers is at least five, the blends segregate into a domain of nearly pure small block copolymer with a small lamellar period and a domain of about equal volume fraction of each block copolymer with a larger lamellar period. The composition and structure of these blends was determined by analyzing the period and area fraction of each phase from plan-view scanning electron micrographs. The lamellae propagate through the thickness of the film. The use of block copolymer blends has potential in block copolymer lithography as a strategy to pattern different period structures in the same film.