Magnetic Control of Morphological Chirality

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Using a vertical superconducting magnet (max. 15 T), we studied magnetic field effects on membrane tube morphology prepared by silicate garden reaction. At zero field, semi-permeable membrane tubes grew upward when metal salts were added to a sodium silicate aqueous solution. In the presence of a magnetic field (15 T, downward) right-handed helical membrane tubes grew along a glass vessel's inner surface when zinc sulfate, magnesium chloride and copper sulfate were added. Referring to membrane tubes' by the names of metal cations used in their preparation, in the case of Mg(II) and Zn(II) membrane tubes, the left-handed helical tubes grew when the field direction was reversed upward. The left-handed helical Mg(II) membrane tubes grew in the magnetic field when a glass rod was placed in a vessel. Mg(II) and Zn(II) tubes, separate from a vessel wall, grew in a twisted shape in the magnetic field. In situ observation of the solution's motion during the reaction revealed that the Lorentz force on the outflow from the opened top of the hollow membrane tube induced convection of the solution near the tube exit, engendering chiral growth of the membrane tubes. Relative orientation of the outflow and a boundary (a vessel wall or glass rod surface) helped to determine the convection's direction. Furthermore, silver dendrite was prepared by the reaction of silver nitrate aqueous solution and metal zinc in magnetic field. The tops of dendrites underwent precession motion during the reaction in magnetic field, indicating the magnetic field induced convection of the solution near the dendrites. The fact strongly suggested the magnetic field affects ionic reactions at liquid and solid interface, inducing chiral growth of solid materials.