Thin films of block copolymer-homopolymer blends with a continuously tunable density of spherical microdomains

A study was conducted to demonstrate the advantage of the through-film structures of block copolymer thin films and the behavior of block copolymer and homopolymer blends in continuously tuning the areal density of micelles from zero up to values comparable to that for a monolayer of neat block copolymer. This was accomplished by control of the film thickness at a constant ratio of block copolymer to homopolymer. The approach relied on the fact that the two dissimilar blocks in the copolymer had preferential interactions with the substrate and with the free surface, leading to complete wetting of each surface by one of the blocks. The approach required that the minority component wetted at least one of the two surfaces. It was demonstrated that the direct connection between micelle areal density and film thickness was a consequence of the fact that the material's composition was uniform on length scales larger than the individual micelle.