Self-Assembled Morphologies of Diblock Copolymer Brushes in Poor Solvents

Self-assembled morphologies of grafted linear AB diblock copolymers are investigated by a simulated annealing method. The copolymers are tethered to a flat substrate by the ends of the A blocks and immersed in a solution that is poor for both. A and B components but exhibits a slight preference for one of the blocks. The morphological dependence of the system on the solvent selectivity, polymer grafting density, and the block lengths is investigated systematically. Phase diagrams for systems with two different grafting densities are constructed for the case where the chains are tethered by the less insoluble blocks. At a moderate grafting density, a variety of complicated morphologies, such as spherical pinned micelles, wormlike micelles, and stripe structures, are observed by varying the block lengths. Other complicated morphologies, such as perforated layers and complete layers, can be formed at a relatively high grafting density. More interestingly, by adjusting the length of copolymer chains and the volume fraction of the more insoluble block, some novel morphologies can be induced, ranging from "spheres-in-stripe" and "rods- in-stripe" structures at the moderate grafting density to "spheres-in-layer" and "rods-in-layer" structures at the higher grafting density. It is also observed that garlic-like and caterpillar-like structures can be obtained only when the solvent is more selective for the top block, consistent with previous theoretical results. Furthermore, the effect of the incompatibility of the two blocks on the structural evolution is also investigated.