Pattern guided structure formation in polymer films of asymmetric blends

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 (lambda = 4 mu m) 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/lambda range, strongly anisotropic morphologies. They show up, for R/lambda similar to 0.5, a weak lambda/2-substructure of smaller PVP droplets in addition to the domains periodic with lambda. The 3:2 blend exhibits morphologies with dominant lambda-structure of PVP ribbons, which encircle PS droplets. For R/lambda similar to 0.5, smaller PS domains are also present but no lambda/2-substructure is formed. The vertical bar chi(E)vertical bar-values of droplet surface density are reduced, as compared to homogeneous substrate, for the 3:2 blend (with vertical bar chi(E)vertical bar -> 0 for R similar to lambda). This effect is absent for the 2:3 mixture. (c) 2005 Elsevier B.V. All rights reserved.