Encoding Latent Domain Orientation in Spray Deposited Block Copolymer Thin Films

The self-assembly of block copolymer (BCP) thin films is a powerful approach to nanopatterning, yet the majority of BCP film research relies on spin coating, which is limited to small, planar substrates (i.e., wafers). Here we report the self-assembly of asymmetric, cylinder-assembling polystyrene-block-poly(4-vinylpyridine) thin films deposited by ultrasonic spraying. "Wet films" are deposited from dilute solutions and film uniformity is regulated by solvent evaporation. Surprisingly, the evaporation time also encodes the latent orientation of cylinders within the films, which fully emerges after domain ordering by solvent vapor annealing. Specifically, short and long drying times facilitate assembly of vertical and horizontal cylinders, respectively. Characterization by grazing-incidence small-angle X-ray scattering (GISAXS) identifies the timescale for polymer vitrification that dictates latent cylinder orientation. This phenomenon can be controlled by substrate heating, forced convection, and solvent formulation. Moreover, it enables encoding of domain orientation on both planar and high-curvature substrates and can be used to deposit films with selective-area orientation control and well-ordered horizontal/vertical cylinder bilayers.