Perpendicular orientation of cylindrical domains upon solvent annealing thin films of polystyrene-b-polylactide

Polystyrene-b-polylactide (PS-PLA) was employed as a precursor to nanoporous thin films containing perpendicular cylindrical channels. Cylinder-forming PS-PLA was spin coated onto Si substrate and solvent annealed using acetone, chlorobenzene and tetrahydrofuran (THF) for different durations. By atomic force microscopy, three types of final morphology were observed at the free surface of the films (PLA surface layer, perpendicular cylinders and parallel cylinders) depending on the type of solvent and annealing time. Well-organized perpendicular domains were obtained by annealing in THF. From this oriented PS-PLA annealed thin films, a mild hydrolysis led to a highly ordered array of perpendicularly-oriented cylindrical nanopores arranged on a hexagonal lattice, rendering the resulting nanoporous mask useful for nanopattern transfer processes. The weak resistance of the film/substrate interface during PLA etching was overcome by UV light exposure prior hydrolysis.