Pattern guided structure formation in polymer films of asymmetric blends

Abstract

Two off-critical blends of poly(2-vinylpyridine) and polystyrene, 2:3 and 3:2 (w:w) PVP:PS, were spin-cast (with varied domain scale R) onto periodically ( λ = 4 μm) patterned substrate. The pattern consisted of two alternating symmetric stripes: Au attracting PVP and neutral self-assembled monolayer. The resulting droplet-type morphologies were recorded with Scanning Force Microscopy and examined with integral geometry approach. PVP-rich islands of the 2:3 PVP:PS films form, for a wide R/ λ range, strongly anisotropic morphologies. They show up, for R/ λ ∼ 0.5, a weak λ/2-substructure of smaller PVP droplets in addition to the domains periodic with λ. The 3:2 blend exhibits morphologies with dominant λ-structure of PVP ribbons, which encircle PS droplets. For R/ λ ∼ 0.5, smaller PS domains are also present but no λ/2-substructure is formed. The | χ E|-values of droplet surface density are reduced, as compared to homogeneous substrate, for the 3:2 blend (with | χ E| → 0 for R ∼ λ). This effect is absent for the 2:3 mixture.