Altering block copolymer (BCP) self-assembly and phase behavior with low-intensity magnetic fields

While block copolymers (BCPs) are promising materials due to their tunable structure and functionality, practical methods for processing BCPs into materials with long-range order remain challenging. We recently discovered magnetic field-induced phase formation in weakly diamagnetic, coil-coil BCPs that cannot be explained by traditional mechanisms of domain alignment. Here, stable ordered phases rapidly form after applying weak magnetic fields to low viscosity solutions of geometrically-isotropic BCP micelles. Magnetorheology confirms that phase formation is accompanied by an increase in modulus of up to six orders of magnitude; phases are stable for hours to days upon field removal. Small angle x-ray scattering indicates that the induced phase depends on BCP characteristics and magnetization time. With increasing magnetization time, structure formation appears to follow multi-step trajectory across the temperature vs. concentration phase diagram, where B-field causes effects similar to increasing T or φ_p. Fully understanding this anomalous assembly phenomenon will afford access to BCP structures and associated lengthscales inaccessible via traditional routes, and provide a platform for developing well-ordered BCP materials under mild processing conditions.