Ultrathin triblock copolymer films on tailored polymer brushes

We fabricated ultrathin poly[styrene-b-butadiene-b-styrenel copolymer (SBS) films deposited on polystyrene brushes. The thickness of the films was kept constant, while the grafting density and molar mass of the grafted polymer layers were varied to reveal the influence of the brush interface on the structure of the films. We examined the surface morphology of the films formed and found a strong effect of the underlying brushes on the formation of the SBS films. The development of a zeroth layer (layer without internal microphase separated structure) of SBS on the top of the grafted layer was observed. Both polystyrene and polybutadiene blocks were present inside the zeroth layer. The first block copolymer layer formed on top of the zeroth layer possessed the surface microstructure typical for the block copolymer in the bulk state. The polymer brushes were actively involved in the formation of the zeroth layer, and the structure of the block copolymer films was influenced by the grafting density and degree of polymerization of the underlying grafted polymer layer. We observed significantly distinct morphologies for the copolymer films of the same thickness deposited on the different polymer brushes. Morphology of isolated islands, holes of different size, and intermediates between islands and holes as well as uniform zeroth layer developed during annealing. Our studies demonstrate that the morphology of ultrathin block copolymer film can be manipulated by the grafting density and molecular mass of the underlying brush.