Macroscopic Alignment of Cylinders via Directional Coalescence of Spheres along Annealing Solvent Permeation Directions in Block Copolymer Thick Films

We reported the long-range perpendicular and horizontal orientation of polystyrene cylinders in polystyrene-b-poly(methyl acrylate) (PS-b-PMA) films with thickness scale from hundreds micrometers to millimeters. Dissolving block copolymer (BCP) in selective solvents forms PS micelles in solution, which could be trapped in films after ordinary solvent casting. Controllable alignment of perpendicular and horizontal cylinders from the directional coalescences of PS spheres along permeation directions of annealing solvent into the film was achieved, i.e., solvent permeating from surface of film led to perpendicular PS cylinders while from edge resulted in horizontal cylinders. Polarizing optical micrographs and mu-beam SAXS confirmed the directional coalescences mechanism during the orientation process and that the cylindrical structure was achieved throughout a macroscopic scale. Solvent components influenced the orientation behavior, and the mixed solvents containing 2540% (volume fraction) methanol were favorable to form highly oriented cylinders.