Balanced Interfacial Interactions for Fluoroacrylic Block Copolymer Films and Fast Electric Field Directed Assembly

Polystyrene-b-poly(2,2,2-trifluoroethyl acrylate)s (PS-b-PTFEAs) are a high-χ block copolymer (BCP) system possessing high potential for fabricating sub-10 nm nanoscopic patterns, however, their thin film implications are limited by the substantially large surface energy difference between the two blocks. Herein, we investigate how to direct the lamellae perpendicular to the substrates and uniaxial along the electric vector via a thermal annealing process. For PS-b-PTFEA films supported on a neutral-like underlying homopolymer mat, we modulate the interfacial interactions of top-coat random copolymers by controlling the molar ratios of S to TFEA units with polarity-switchable maleic anhydride. Intriguingly, the neutral top-coat interactions for PS-b-PTFEA films occur at a highly asymmetric composition with a larger S fraction to suppress lower surface energy of the PTFEA block. Under such a neutral confinement on both the top surface and bottom simultaneously, the BCP films subjected to a lateral electric field exhibit a directed orientation of perpendicular lamellae along the electric vector. Notably, a short period (5 min) of treatment is enough for the PS-b-PTFEA film to produce uniaxial alignment of sub-10 nm-scale perpendicular lamellae under a direct current potential of 25 V/μm. This fast directed assembly kinetics is likely because of rapid chain diffusion of short segments in synergy with high dielectric contrast between the two components.