Enhanced Self-Assembly of Metal Oxides and Metal-Organic Frameworks from Precursors with Magnetohydrodynamically Induced Long-Lived Collective Spin States

摘要

Low energy permanent magnetic fields (0.5T) applied in hydrodynamically turbulent conditions are observed to enhance self-assembly of materials with magnetically frustrated spin systems (spin-glass, spin-ice or spin–liquid). This effect is demonstrated for the crystallization of vanadium oxide nano-scrolls, manganese oxide nano-tubes and HKUST-1 type Cu3(BTC)2.3H2O Metal-Organic Framework. Crystallization of these spin systems involves spin coupling and alignment of initially isolated paramagnetic metal ions, respectively V(IV), Mn(IV) and Cu(II) into molecular precursor units that self-assemble to the final material. The electromagnetic and hydrodynamic forces applied during magnetohydrodynamic precursor treatment induce a long lived state of collective spin order by the resonant coupling of magnetic field and turbulent structured flow. This altered magnetic alignment in the molecular precursor units consequently assist the self-assembly process resulting in optimised morphology. The presented experimental setup enables precise control over the magnetohydrodynamic conditions during synthesis, essential for elucidation the detailed mechanism.