Observed Surface Energy Effects in Confined Diblock Copolymers

By using thin layers of random copolymer, we have varied the specificity of block-wall interactions for films of diblock copolymer confined between parallel walls. For highly specific interactions (bare walls), one block component segregates to both interfaces, and the frustration due to incommensuration between film thickness and the diblock's bulk period is accommodated by the formation of layers parallel to the walls with perturbed period. In contrast, reduced specific interactions (random-copolymer-coated walls) allow the frustration to be accommodated by perpendicular ordering of the diblock, such that both block components are present at the walls.