Vertical Segregation in Planar Multiblock Copolymer Brushes Induced by Collapse in a Nonselective Solvent

A planar polymer brush formed by grafted linear macromolecules of a symmetric AB-multiblock copolymer and immersed in a nonselective solvent is studied theoretically by using Scheutjens-Fleer self-consistent field modeling. The brush collapse upon deterioration in solvent quality is considered, with a focus on the effect of block incompatibility on the brush structure. It is shown that when the blocks are incompatible, the collapse of the brush leads to intrabrush microphase segregation, with the formation of alternating layers enriched in A and B units within the brush. The free ends' distribution in the layered brush is multimodal, which is a novel feature for monodisperse polymer brushes. It was found that at pronounced incompatibility between blocks, partial localization of solvent molecules at the boundaries between the A and B layers takes place, leading to oscillations in the polymer volume fraction profile. Deterioration in the solvent quality also leads to a decrease in the total number of layers formed in the brush. Longer blocks and higher grafting densities promote a more pronounced layered structure, while increasing incompatibility between blocks leads to brush reswelling.