Morphology of Block Copolymer and Bottlebrush Blends in Thin Films and Bulk

The structure, properties, and assembly kinetics of block copolymers (BCPs) can be tuned through the use of additives. A variety of additives have been explored, including homopolymers, nanoparticles, salts, and other small molecules. When homopolymers are added to a BCP their distribution within the BCP depends on the relative molecular weight between the homopolymer and BCP, with high molecular weights generally leading to macrophase separation. Bottlebrush polymers, consisting of short sidechains arranged along a linear backbone, present an interesting case where the overall molecular weight is large, but the sidechains can be short relative to the BCP. Small angle X-ray scattering measurements are used to explore the bulk structure of BCP/bottlebrush blends, and the results are placed in context with well known examples of BCP/homopolymer blends. The self-assembly of thin films are interrogated with a combination of AFM, GISAXS and soft X-ray scattering. The thin films show a thickness dependence of the morphology over a critical volume fraction of the bottlebrush additive, and the structure suggests the bottlebrush distributes differently in the thin film compared to the bulk. The role of the bottlebrush on the assembly kinetics is also investigated.