Self-assembling Process of Block Copolymers at the Solid–Polymer Melt Interface: Fundamentals and Applications

We present new pieces of experimental findings on the self-assembling process of block copolymers (BCPs) on nonneutral solid substrate surfaces. The key to this event is the concurrent physisorption of preferred blocks and nonpreferred blocks on the surface. We uncover two different kinds of BCP chains adsorbed on the solid surface using an optimized solvent-rinsing approach. One is the inner strongly adsorbed BCP chains in which all constituent blocks lie flat and form a two-dimensional network-like structure regardless of their chain architectures, microdomain structures, and interfacial energetics. The other is outer “loosely adsorbed BCP chains,” which form a poorly packed perpendicularly oriented microdomain structure on the substrate surface. The loosely adsorbed BCP chains act as seeds and promote poor perpendicularly oriented microdomains in a single BCP thin film. Interestingly, this substrate-field effect propagates into the film interior via chain entanglements between neighboring unadsorbed chains in the matrix and the loosely adsorbed chains up to a distance of ∼70 nm from the substrate surface. Finally, a new surface modification approach prevents the development of the undesirable substrate-field effect. We demonstrate that homopolymer chains composed of one of the constituent blocks adsorbed on the solid substrates act as a “structurally neutral” surface coating against both blocks.