2025 AIChE Annual Meeting

Self-Assembly of FeOx Nanoparticles into Binary Superlattice

Magnetic nanoparticles, like iron (III) oxide nanoparticles (IONPs), have unique tunable properties and a stronger magnetic moment compared to their bulk materials, making them promising candidates for applications such as imaging agents in the biomedical field or in targeted drug delivery. These nanoparticles also have an intrinsic tendency to self-assemble into superlattices, or even binary superlattices in the presence of secondary smaller nanoparticles, to maximize the entropy.

The scale of superlattices, often called “man-made” solids, convert nanoscale building blocks into metamaterial from the bottom up with controllable surface and magnetic properties. To understand fundamental self-assembly patterns and be able to predict non-equilibrium state packing behaviors, effects of static and rotating magnetic fields on the assembly must be studied. An important requirement for the formation of binary superlattices is the colloidal stability of the nanoparticles, a narrow size distribution, and a compatible size ratio between the larger and smaller nanoparticles. Larger iron oxide nanoparticles are desirable to maximize the effect of the magnetic field on the particles.

Here, numerous synthesis methods of IONPs with variations in synthesis parameters are tested to determine the optimal particle size and size distribution for the self-assembly study. In addition, materials with distinct degrees of electron density and of different sizes, ranging from 8 nm to 10 nm in diameter, were tested to form binary superlattices. Large iron oxide nanoparticles with a diameter of 20.3 nm and high colloidal stability were successfully synthesized and organized into packed superlattice structures when solvents were dried. Under the mixture with CdSe nanocrystals, they formed disclinations, packing into star-like shapes.