(402d) Preparation of Structured Bio-Inspired Composite Materials through Magnetic Control of Sol-Gel Phase Transitions

Nanocomposites are an important class of materials, with unique properties resulting from the unique combination of the matrix and the dispersed phase. Being able to control the structure of the disperse phase is paramount to control the final properties of the material. Here we present a new strategy for the preparation of bioinspired composite materials, by using magnetic colloids to control the structure of a silica gel phase by magnetically manipulate the sol-gel phase transition. The gel phase has then be used as a skeleton for the preparation of a polymer-inorganic hybrid material. Magnetic colloids were added to the silica sol precursor solution, and a magnetic field was applied during the sol−gel transition. A static field led to a fiber-like structure, with silica fibers aligned in the direction of a field. Conversely, when exposed to a rotating magnetic field, magnetic colloids organized in layers parallel to the plane of rotation of the field and template the growing silica phase, resulting in a layered anisotropic silica, reminiscent of the inorganic structure of nacre. The final nanocomposite materials have been created by filling the porous structure with a monomer, leading to an elastomer upon polymerization. Compression tests of the structured composite show that their mechanical properties far exceed those of nonstructured composite materials with an identical chemical composition. Furthermore, more complex silica structures have been obtained by first creating a structured silica gel, and then impregnating it with a second sol solution containing magnetic colloids, and applying a magnetic field in a different direction. In this case, silica gels with a fiber structure connected by perpendicular rods connecting them, or layered silica gels with rods perpendicular to the layer and connecting them were obtained, eventually leading to even stronger composite materials, with defined anisotropy and with a complex architecture could be prepared. These structures are reminding of the complex architecture of bones, shells and other biological materials. In the attached figure, SEM images of some of the structures obtained by the magnetic control of the sol-gel phase transitions are showcased.

References

[1] “Preparation and Machine-Learning Methods of Nacre-like Composites from the Self-Assembly of Magnetic Colloids Exposed to Rotating Magnetic Fields”, Joelle Medinger, Miroslava Nedyalkova, Marco Furlan, Thomas Lüthi, Jürgen Hofmann, Antonia Neels, Marco Lattuada, ACS Applied Materials & Interfaces, 13, 8040-48052 (2021)

[2] “Fabrication of anisotropic porous silica monoliths by means of magnetically controlled phase separation in sol–gel processes”, Marco Furlan and Marco Lattuada, Langmuir, 28, 12655-12662 (2012)