(168b) Batch and Continuous-Flow Separation of Spions Under a Quadrupole Field

Superparamagnetic iron oxide nanoparticles (SPIONs) compose a class of magnetic nanoparticles (MNPs) that have been increasingly studied as pivotal agents in the biomedicine, environmental remediation, and theranostics fields [1-4] due their distinctive chemical and physical properties such as high magnetization, ease of functionalization, and low toxicity, to name a few. Magnetic separation is an essential step of a diverse range of applications that involve a binding entity to the MNPs’ surface. In this context, separation techniques based on field-induced magnetophoresis have proven to be efficient. Still, the separation of MNPs within a liquid phase becomes more challenging as their size is reduced, mainly due to the predominance of random Brownian motion. The use of horizontal magnetic gradients (i.e. perpendicular to gravity) has been proposed and explored as a promising alternative to achieve the separation of ultra-small (< 30 nm) MNPs, with increasing evidence from experimentations with SPIONs [5,6]. This approach benefits from a combined effect of particle self-assembly, due to dipole-dipole interactions, and potential particle-fluid interactions. Recent numerical studies and X-ray scattering data brought evidence of magnetic separation through non-cooperative mechanisms of ultra-small SPIONs [7]. Particles in the proximity of a magnetic pole (i.e. initially non-emerged into the magnetic gradient) were observed to undergo magnetophoresis as well, eventually accumulating at a collection plane. To further investigate this behavior, this study aims to optimize the separation of ultra-small SPIONs in batch and decipher the separation mechanisms using numerical modeling and SAXS analysis and implement, for the first time, the continuous-flow separation of these materials.In the experimental portion of this study, we will perform both batch and continuous-flow separations of ultra-small SPIONs through our custom quadrupole magnetic sorter (QMS) as the source of the horizontal, constant magnetic gradient (, ). Briefly, our custom QMS consists of a specific magnetic arrangement of four permanent magnets that revolve around a bore, throughout which the quadrupole magnetic gradient manifests. Independent variables will consist of different particle sizes (, nm) – assuming that particles are spherical in shape with a homogenous size distribution – and the aqueous dispersion’s initial concentrations (, ). Specifically for the continuous-flow case, dispersion flowrate (, ) will be considered, which is consistently related to manipulating the dispersion velocity (, ) as it travels through the QMS bore. For the numerical portion, we will employ the finite-element method (FEM) simulation software, COMSOL Multiphysics 6.2, to model the magnetic field generated by the QMS and to predict the trajectory of the particles inside the system [8,9]. This model will comprehensively consider magnetophoretic, gravitational, Brownian, and fluid drag forces.We intend to elucidate the role of cooperative magnetophoresis, as well as particle-fluid interactions, in the separation processes both experimentally and numerically. Through these experiments, we intend to deepen the discussion and understanding of novel mechanisms through which magnetic separation of ultra-small SPIONs becomes possible and further develop the field toward more efficient magnetic separation systems.

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