Abstract
The controlled agglomeration of superparamagnetic iron oxide nanoparticles (SPIONs) was used to rapidly switch their magnetic properties. Small-angle X-ray scattering (SAXS) and dynamic light scattering showed that tailored iron oxide nanoparticles with phase-changing organic ligand shells agglomerate at temperatures between 5 °C and 20 °C. We observed the concurrent change in magnetic properties using magnetic particle spectroscopy (MPS) with a temporal resolution on the order of seconds and found reversible switching of magnetic properties of SPIONs by changing their agglomeration state. The non-linear correlation between magnetization amplitude from MPS and agglomeration degree from SAXS data indicated that the agglomerates' size distribution affected magnetic properties.
Highlights
The agglomeration of noble metal and semiconductor nanoparticles dispersed in non-polar solvents has recently been studied in detail.[1,2,3,4,5] Such non-polar particles are not dominated by electrostatic interactions
We studied the change of magnetic properties in superparamagnetic iron oxide nanoparticles (SPIONs) upon thermally induced agglomeration
We suggest that the magnetization amplitude of Neel-dominated SPIONs is strongly affected by particle–particle interactions upon agglomeration that change the magnetic relaxation with respect to an external alternating magnetic eld.[26]
Summary
The agglomeration of noble metal and semiconductor nanoparticles dispersed in non-polar solvents has recently been studied in detail.[1,2,3,4,5] Such non-polar particles are not dominated by electrostatic interactions. Complete reversibility was achieved upon using smaller and less polydisperse iron oxide nanoparticles that we prepared as described in previous work.[22] We used temperature-dependent SAXS to follow the agglomeration of these samples and found no sign of remaining agglomerates (ESI Fig. S5†).
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