(569d) Magnetic Self-Assembly of Superparamagnetic Iron Oxide Nanoparticles Studied By in-Situ Small Angle X-Ray Scattering

With the rapid development and significant improvement of nano-material synthesis technologies, a series of superparamagnetic iron oxide nanoparticles (SPIONs) have been produced with special physical properties, such as high surface to volume ratio, biocompatibility and superparamagnetism. Nevertheless, due to the nanometric size of SPIONs, the magnetically driven isolation method to separate those particles from the media is difficult, considering the fact that the Brownian motion and viscous drag are the two key factors that hinder the magnetic motion of the particles.

In our previous work, we reported the ability to recover 5, 15 and 30 nm particles by applying external magnetic fields and gradients through magnetic agglomeration and sedimentation. Our experimental data suggest that the particles agglomerated due to dipole-dipole interactions. The separation process was finally accomplished by the sedimentation of aggregated particles. However, the nano-structural conformation of agglomerated particles when applying an external magnetic field and the mechanisms behind the separation processes are not fully understood.

In order to gain insight into the separation mechanisms, and more specifically, to unravel the SPIONs magnetic aggregation and sedimentation process, we performed the in-situ Small Angle X-ray Scattering (SAXS) analysis, which is an extremely powerful characterization tool that can provide precise structural information of the particle agglomeration. The in-situ analysis tracked the dynamic evolution of the particle diameter, volume fraction as well as particle number density. A special magnetic separation sorter was used, allowing the X-ray to pass through the tubing containing the particle suspension while being magnetized by the external field. Multiple variables and parameters were studied, including operation time, the magnetic field gradient and field intensities.