Electric Field Induced Sphere-to-Cylinder Transition in Diblock Copolymer Thin Films

An electric field induced sphere-to-cylinder transition in thin films of asymmetric polystyrene-b-poly(methyl methacrylate) diblock copolymers was observed. In the absence of an applied electric field, thin films of the asymmetric diblock copolymer consisted of layers of spherical microdomains with poor in-plane long-range ordering. Under a ∼40V/μm applied electric field, hexagonally packed cylindrical microdomains normal to the surface were found. Cross-sectional transmission electron microscopy images of the intermediate stages of the alignment indicated that, under an electric field, the asymmetric diblock copolymer formed spherical microdomains that were deformed into ellipsoids and, with time, interconnected into cylindrical microdomains oriented in the direction of the applied electric field. Simulations suggest that improved long-range order of the cylindrical microdomains could be achieved by cycling the electrical field.