Synthesis and Characterization of SiO₂/(PMMA/Fe₃O₄) Magnetic Nanocomposites

Abstract

Magnetic silica nanocomposites (magnetic nanoparticles core coated by silica shell) have the wide promising applications in the biomedical field and usually been prepared based on the famous Stöber process. However, the flocculation of Fe 3 O 4 nanoparticles easily occurs during the silica coating, which limits the amount of magnetic silica particles produced in the Stöber process. In this paper, PMMA/Fe 3 O 4 nanoparticles were used in the Stöber process instead of the “nude” Fe 3 O 4 nanoparticles. And coating Fe 3 O 4 with PMMA polymer beforehand can prevent magnetic nanoparticles from the aggregation that usually comes from the increasing of ionic strength during the hydrolyzation of tetraethoxysilane (TEOS) by the steric hindrance. The results show that the critical concentration of magnetic nanoparticles can increase from 12 mg/L for “nude” Fe 3 O 4 nanoparticles to 3 g/L for PMMA/Fe 3 O 4 nanoparticles during the Stöber process. And before the deposition of silica shell, the surface of PMMA/Fe 3 O 4 nanoparticles had to be further modified by hydrolyzing them in CH 3 OH/NH 3 ˙H 2 O mixture solution, which provides the carboxyl groups on their surface to react further with the silanol groups of silicic acid.