(294d) Mimicking Nacre through Magnetically Driven Self-Assembly of Colloids

Nature’s intelligent design of composite materials leads to enhanced mechanical properties compared to the individual constituents, which can for example lead to a combination of high stiffness and toughness. Nature design principles have inspired scientists to fabricate reinforced synthetic materials by mimicking the architecture of biological systems. Nacre is one of the most studied systems. It is a composite material formed of alternating layers of inorganic aragonite platelets intercalated by a biopolymer. Nacre displays remarkably high mechanical properties going far beyond the rule of mixture of its constituents.

We tried to mimic this layered composite structure using silica as inorganic material. In order to obtain a layered porous and anisotropic silica network, we modified the conventional sol-gel process, which leads to porous silica monoliths, by adding superparamagnetic iron oxide nanoparticles (SPIONS) and applying an external rotating magnetic field during the sol-gel transition. The magnetic nanoparticles will self-assemble into layered structures in the presence of a high frequency rotating field, aligned in the plane of rotation of the field. Silica having an affinity for the iron oxide nanoparticles will nucleate on them adopting the same structure as the SPIONS, which act as smart templates to dictate the final structure of the monolith, which is permanently fixed after gelation. The final inorganic-organic nacre inspired composite is created by filling the porous structure with a polymer. Compressions tests of the platelet-structured composite show the desired increase of the mechanical properties of the silica monolith.