Bottlebrush Block Copolymer Assembly in Ultraconfined Films: Effect of Substrate Selectivity

Ultraconfined block copolymer films present nonbulk structures that are highly sensitive to film thickness and are strongly influenced by the wetting properties of the substrate. Here, we describe the self-assembly of bottlebrush block copolymers with varying side-chain lengths on different types of substrates. Our results show a pronounced influence of the nature of the substrate on the self-assembled morphology and the surface patterns that evolve during solvent-vapor annealing. In particular, we observe by experiments and simulations a transient, substrate-driven morphology of cylinder-like structures obtained in films of doubly symmetric (i.e., the backbone and side chains) bottlebrush block copolymers despite the general tendency of these polymers to form lamellar structures. The insights gained from this study highlight the ability to use the substrate chemistry for inducing the formation of unique morphologies in bottlebrush block copolymer films.