(342e) Novel Porous Ceramic Materials Via Magnetically Driven Self-Assembly of Non-Magnetic Nanoparticles

The preparation of porous materials via self-assembly of nano- and microparticles is a topic of great scientific and technological relevance. Applications for such materials can be found in many areas, such as chromatography, membrane production, catalyst supports, bio-inspired materials, and scaffolds for tissue engineering.

Conventional materials, which can be prepared from colloidal suspension of polymers or ceramics, have usually a random porous structure. The preparation of these materials with better organized pores is of paramount interest for many applications.

In this work we introduce a new technique for the preparation of porous materials with anisotropic structure. This new method takes advantage of the alignment in the presence of a magnetic field of non-magnetic colloidal nanoparticles, either polymeric or ceramic (e.g. silica, alumina), dispersed in an aqueous highly stable ferrofluid. Once the magnetic field is applied, the non-magnetic nanoparticles act as magnetic holes, i.e., they acquire a magnetic moment in the opposite direction to that of the external field. These moments generate dipolar interactions capable of aligning non-magnetic particles in the direction of the applied field.^[1]

The obtained structures can be frozen by adding a water-soluble monomer, a crosslinker and an initiator to the aqueous solution, so that once the structure is formed a free radical polymerization process can be utilized to produces a hydrogel that locks it. Once the obtained anisotropic structure is blocked inside the hydrogel, the ferrofluid can be removed by immersing the hydrogel in a concentrated hydrochloric acid solution. The anisotropic structure can then be hardened by depositing via a sol gel process either the same material of the nanoparticles or a different one, by simply immersing the monolith in a solution of the sol-gel precursor. After removing of the hydrogel by thermal treatment a hard porous monolith can be obtained. The resulting materials have a complex and organized structure, which was studied and characterized using SEM microscopy and mercury porosimetry.

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