Overcoming Interfacial Interactions with Electric Fields

Electric fields have been shown to orient nanoscopic domains laterally in thin copolymer films effectively. To achieve an orientation normal to the surface, interfacial interactions impose a barrier. Using asymmetric diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) having cylindrical microdomains, a threshold electric field strength Et was found above which complete orientation of the cylindrical domains was achieved. This threshold field strength was independent of film thickness (for films ∼10−30 μm thick) and could be described by the difference in interfacial energies of the components. At field strengths slightly below Et a coexistence of the domains parallel and perpendicular to the electrode surface was found which is consistent with the introduction of defects via undulations in the structure as one proceeds away from the surface.