Magnetic Control of Morphological Chirality

使用垂直超导磁体(最大15T)，研究了磁场对硅酸盐花园反应制备膜管形貌的影响。在零场下，当金属盐加入水玻璃水溶液中时，半透膜管向上生长。在向下磁场(15T)作用下，当加入硫酸锌、氯化镁和硫酸铜时，右手螺旋膜管沿玻璃容器的内表面生长。膜管是指在制备过程中使用的金属阳离子的名称，在镁(II)和锌(II)膜管的情况下，左旋螺旋管随着磁场方向的反转向上生长。当玻璃棒被放置在容器中时，左旋螺旋镁(II)膜管在磁场中生长。与管壁分离的镁(II)和锌(II)管在磁场中以扭曲的形式生长。在反应过程中对溶液运动的原位观察表明，中空膜管开口顶部流出的洛伦兹力诱导了溶液在管口附近的对流，导致膜管的手性生长。外流和边界(管壁或玻璃棒表面)的相对取向有助于确定对流的方向。在此基础上，利用硝酸银水溶液与金属锌在磁场中的反应制备了银树枝晶。在磁场作用下，枝晶顶端发生进动运动，表明磁场在枝晶附近诱导了溶液的对流。这一事实强烈地表明，磁场影响液-固界面上的离子反应，诱导固体材料的手性生长。

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.