(634e) Magnetic Assisted Self-Assembly

Materials produced via self-assembly of nano- and micro-particles are becoming of great interest in many applications, such as in chromatography, membrane preparation, catalyst supports, bio-inspired materials, and scaffolds for cell growth. These materials can be prepared from colloidal suspensions of polymer or ceramic particles like silica or alumina. These materials are very rigid and have a usually a random porous structure. On the other hand, the preparation of materials with better organized pore structure is generally much more challenging. In a previous work we have introduced a new method called magnetic gelation^[1] which allows us to obtain porous polymeric material with anisotropic structure. This process, although effective, is limited by the need to have magnetic nanocrystals incorporated inside the nanoparticles to be aligned. In this work, we introduce a different technique to produce anisotropic materials called magnetic assisted self-assembly. The new method allows one to use almost any material in the form of an aqueous colloidal dispersion of electrostatically-stabilized particles, such as ceramics (e.g. silica, alumina), or polymer nanoparticles, which are assembled in the presence of a magnetic field in a water based ferrofluid. First of all, a colloidal suspension of the material is prepared using a water-based ferrofluid as dispersant, followed by coagulation of the dispersion in the presence of an external magnetic field by increasing the ionic strength of the solution. Once the magnetic field is applied, the non magnetic particles act as magnetic holes, i.e. they acquire a magnetic moment in the opposite direction to that of the ferrofluid. These moments generate dipolar interactions capable to aligning non-magnetic particles in the direction of the applied field.^[2] The obtained materials have been first hardened via reactive gelation (polymer) or sintering (ceramics) and then their resulting structure was studied and characterized using SEM microscopy and torque magnetometry.

[1] M. Furlan, B. Brand, M. Lattuada, submited to JACS.

[2] A. T. Skjeltorp, Phys. Rev. Lett. 1983, 51, 2306.