New insight into self-assembly of block copolymers at the solid-polymer melt interface

I present new pieces of experimental findings on the self-assembling process of block copolymers (BCPs) near nonneutral silicon (Si) substrate surfaces. The key is concurrent physisorption of preferred blocks and non-preferred blocks on the surface. Using an optimized solvent-rinsing approach, we successfully uncovered two different kinds of adsorbed BCP chains: one is the inner strongly adsorbed BCP chains where all constituent blocks lie flat and form a two-dimensional percolating network structure regardless of their chain architectures, microdomain structures, and interfacial energetics. The other is outer "loosely adsorbed chains" which form a poorly packed perpendicularly oriented microdomain structure. I will show that the inner microdomain structures and orientations of BCP thin films are negatively impacted by the loosely adsorbed BCP chains. Interestingly, this undesirable substrate-field effect propagates into the film interior up to the distance of ~ 70 nm. Finally, a new surface modification approach to prevent the substrate-field effect is proposed. I will demonstrate that homopolymer chains composed of one of the constituent blocks adsorbed on the Si substrates act as a “structurally neutral” surface coating for directed self-assembly of block copolymer thin films.