Synthesis and characterization of nearly monodisperse superparamagnetic (Fe₃O₄/Poly(methyl methacrylate))-SiO₂ nanoparticles with raspberry-like morphology

Abstract

Uniform and nearly monodisperse superparamagnetic Fe3O4/Poly(methyl methacrylate) (core)/SiO2 (shell) nanoparticles with raspberry-like morphology and high saturation magnetization were prepared in three different steps. At first, a facile, one-shot procedure to synthesize hydrophobic Fe3O4 nanoparticles through a modified co-precipitation method was implemented. Based on the hydrophobic interactions, these nanoparticles were used directly in a mini-emulsion polymerization resulting in encapsulation with PMMA. Then, for the covering with a silica shell, the surfaces of the Fe3O4/PMMA nanospheres were hydrolyzed in alkaline media and became hydrophilic through hydrolyzation. In the last step shell deposition of the Fe3O4/PMMA nanospheres through a modified Stober method was implemented. The surface morphology was investigated by scanning electron microscopy (SEM) and the core-shell structure and the prepared products’ diameters were measured by transmission electron microscopy (TEM); the size of the magnetic nanospheres was approximately 83 nm. Vibrating sample magnetometry (VSM) showed high magnetic saturation and superparamagnetic characteristics of the particles. Thermogravimetric analysis (TGA) was used as a supplementary test and, based on the mass loss at high temperature (600°C), the magnetic (Fe3O4) and non-magnetic content (PMMA) of the Fe3O4/PMMA nanospheres was measured as 81 and 19%, respectively. The narrow polydispersity of the nanospheres, measured by dynamic light scattering (DLS), was approximately 0.101. In every preparation step, the synthesized products were characterized by Fourier transform infrared (FTIR) spectroscopy. Our study focused on designing two-layered magnetic nanoparticles with drug delivery potential using two-layer encapsulation based on the hydrophobic and hydrophilic surface characteristics of the PMMA core and silica shells, respectively.