Orientation-Dependent Order–Disorder Transition of Block Copolymer Lamellae in Electric Fields

Electric fields have been shown to stabilize the disordered phase of near-critical block copolymer solutions. Here, we use in situ synchrotron small-angle X-ray scattering to examine how the initial orientation of lamellar domains with respect to the external field (φ) affects the shift in the order–disorder transition temperature (T_ODT) of lyotropic solutions of poly­(styrene-b-isoprene) in toluene. We find a downward shift of the transition temperature, which scales with lamellar orientation as ΔT_ODT ∼ cos² φ, in accordance with theory.