Large area orientation of block copolymer microdomains in thin films via directional crystallization of a solvent

A fast method for inducing alignment of microdomains in noncrystalline block copolymers is presented. The method is based on the use of crystalline organic materials, which are solvents for the block copolymers above their melting temperatures, and, when cooled and directionally crystallized, act as a substrate on which thin films of the block copolymers are formed. Both lamellar and cylindrical type microdomains in a symmetric polystyrene-block-poly(methyl methacrylate) diblock copolymer and in an asymmetric polystyrene-block-polyisoprene respectively are globally aligned using either benzoic acid (BA) or anthracene (AN) as the crystallizable solvent. The fast directional solidification during the phase separation leads to alignment of the intermaterial dividing surface (IMDS) of both types of microdomains parallel to the fast growth direction of BA and AN crystals (b axis direction in both cases). Depending on film thicknesses, the block copolymers show various microdomain orientations such as vertical lamellae and parallel and perpendicular cylinders to the substrate. With respect to the processing methods currently used to induce orientation in block copolymers, our method allows attainment of ordered patterns over regions larger than 50 μm² within a few seconds without annealing.