Dipolar interactions among magnetic dipoles of iron oxide nanoparticles dispersed in mili-size hydrogel objects

DANIEL ACTIS; GUILLERMO ARTURO MUÑOZ MEDINA; LAURA SÁNCHEZ; ÁLVARO VELÁSQUEZ

Poznan

Congreso; 24th Soft Magnetic Materials; 2019

Institute of Molecular Physics

This contribution is devoted to quantify the modification of the magnetic response of iron oxide nanoparticles (NPs) dispersed in a hydrogel, due to dipole-dipole interactions, when the geometry and density of their spatial distribution is modified in a controlled manner. This problem is of crucial importance for the application of magnetic hydrogels. This happens because the hydrogel expands and small pieces of it may aggregate, thus modifying sensibly the NPs distribution. Millimetric-size, spheroid-like hydrogel objects were synthesized through a one pot route. The experimental strategy was based on two experiments. In the first one hydrogel swelling by hydration was used to modify the intensity of dipole-dipole interactions, by varying inter-dipole mean distance [1]. In the second one, chain and disk-like arrays of spheroids were studied and compared with an isolated spheroid. The magnetic response of these NPs ensembles was recorded by VSM magnetometry, ac susceptibility and Specific Absorption Rate (SAR) of energy under radiofrequency irradiation. The MFISP model, which evaluates the effect of dipolar interactions by introducing and defining an effective demagnetizing tensor [1,2] was used to analyse the results. Alternatively, a model based on a semi-discrete approach was developed and applied. The results demonstrate that density and anisotropy of the NPs distribution affects the magnetic susceptibility of the NPs ensembles consistently with the theoretical expectations of the models. These observations are of importance in applications of magnetic NPs, as for example in vitro and in vivo magnetic hyperthermia, where geometry and density of NPs distribution is highly determined either by culture or tissue specific features.