Authors: M. Furlan, M. Lattuada
Affilation: University of Fribourg, Switzerland
Pages: 506 - 509
Keywords: self-assembly, magnetic rods, magnetic platelets, sol-gel, composite material, magnetic field
In this work, we propose a new versatile self-assembly technique to obtain large quantities of silica-based magnetic nano and micro-rods and of magnetic microplatelets, which can be easily oriented by weak magnetic fields. Our process consists in the preparation of silica monoliths by a sol-gel process, with the addition of magnetic nanocolloids as templates in the presence of a magnetic field. Two magnetic field configurations have been explored: 1) static magnetic fields, which lead to the self-organization of magnetic nanocolloids into long tubular structures; 2) rotating magnetic fields, which drive the assembly of the particles into two-dimensional sheet-like structures. The diameter of the rods and the thickness of the platelets can be precisely controlled during sol-gel. The unique microstructure of the silica monoliths confers them strong mechanical anisotropy, either one or two-dimensional. This microstructure enables one to selectively break the monoliths and recover either magnetic nano- and micro-rods or magnetic micro-platelets through the application of a strong ultrasonication. The length of the rods and the area of the platelets are determined by the ultrasonication time and intensity. Both rods and plates have been incorporated into rubbery polymer matrices, leading to rod-like and nacre-like composite materials.