Beyond alignment: a novel mechanism for developing well-ordered block copolymer materials via low-intensity magnetic fields

Prior work in the directed assembly of block copolymers (BCPs) via magnetic fields has primarily relied on the alignment of BCP chains or phases in bulk. In this work, the application of low-intensity magnetic fields (B ≤ 0.5 T) to poloxamer solutions yields a remarkable solvent-mediated disorder-to-order transition, not reliant on alignment mechanisms. In situ magneto-rheology demonstrates this ordering transition is accompanied by substantial increase in shear modulus, surpassing the effects of thermally-induced ordering by several orders of magnitude. Subsequent magnetization induces order-to-order transitions, from cubic to cylindrical micelle packings. The mechanism underlying this ordering behaviors is illuminated via a combination of magnetorheology, small- and wide-angle X-ray scattering, differential scanning calorimetry, and vibrational spectroscopy. This study further quantifies significant reductions in micelle size and aggregation numbers when compared to temperature- and concentration-induced ordering. Overall, low-intensity magnetic fields (B-fields) exert a profound influence on polymer-solvent interactions within this aqueous BCP system, providing the driving force for this anomalous magnetically-induced ordering.