Processive Pathway of Solvent-Induced Self-Assembly of PS-b-P2VP Thin Films

Block copolymer thin films enable precise control of surface morphology, nanopattern geometry, and interfacial chemistry via self-assembly. We investigate the impact of solvent-block copolymer interactions on self-assembled structures in thin films. Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) with a molecular weight of Mw = 199 kDa and a PS-to-P2VP block ratio of 102k/97k was selected as the model system. Firstly, PS-b-P2VP is dissolved in toluene to form PS-shell spherical micelles, which are then spin-coated onto a Si substrate to create a film with a thickness of approximately 100 nm. Starting from as-cast micellar morphologies, we compare methods of solvent vapor annealing and direct immersion annealing by varying the solvent selectivity, concentration, and exposure time. AFM, SEM, and GISAXS quantify surface morphology, domain orientation, ordering, domain spacing, and roughness. Ellipsometry is used to measure swelling and deswelling. Combination of contact angle measurements, XPS, and FTIR are used to determine the surface chemistry composition. We observe route-dependent non linear morphology transitions under 2D confinement thin films including micelles to lamellae and other unique nanoporous assemblies that differ from bulk. These structures can be stabilized after annealing. Our findings shed light on structure evolution and stabilization in confined thin films and offer access to diverse morphologies and structures beyond standard annealing methods.