Effects of Confinement on the Structure of Bottlebrush Polymers in Thin Films

Bottlebrush block copolymers (BCPs) have intriguing potential in nanopatterning and photonics applications as they lack entanglements and can rapidly assemble. As a result, bottlebrush BCPs can self-assemble with periodicities over 100 nm, a length scale which is challenging to achieve with linear BCPs. Nanopatterning applications will require confinement of bottlebrush BCPs in thin films, where their behavior is still poorly understood. The assembly of bottlebrush BCPs of polystyrene-b-poly(lactic acid) (PS-b-PLA) in thin films was studied using a combination of techniques. Blade coating was used to produce a controlled thickness gradient so that the impact of the thickness/periodicity ratio can be studied. The resulting structures were evaluated using a combination of atomic force microscopy (AFM), grazing incidence X-ray scattering (GISAXS) and resonant soft X-ray scattering (RSoXS). The effects of solvent and annealing conditions on the resulting morphologies was also explored.