Synthesis and electromagnetic properties of polyaniline-coated silica/maghemite nanoparticles

Polyaniline coated silica/maghemite nanoparticles (PANI/SiO2/γ-Fe2O3 composites) were synthesized by the combination of a sol–gel process and an in-situ polymerization method, in which ferrous and ferric salts as well as tetraethyl orthosilica (TEOS) acted as the precursor for γ-Fe2O3 and silica, respectively. As a result, the SiO2/γ-Fe2O3 particle showed a core-shell structure, with γ-Fe2O3 as the magnetic core and silica as the shell of the particle. The shell thickness can be controlled by changing the TEOS concentration. The PANI/SiO2/γ-Fe2O3 composites revealed a multilayer core-shell structure, where PANI is the outer shell of the composite. The doping level and the conductivity of PANI/SiO2/γ-Fe2O3 composites decreased with increasing the TEOS content due to the presence of the less coated PANI on the SiO2/γ-Fe2O3 core at higher TEOS content. For a SQUID analysis at room temperature, all γ-Fe2O3 containing composites showed a typical superparamagnetic behavior. The saturation magnetization of SiO2/γ-Fe2O3 nanoparticles decreased with increasing the TEOS content due to the increase in silica shell thickness, while the saturation magnetization of PANI/SiO2/γ-Fe2O3 composites also decreased with increasing the TEOS content, which is attributed to the lower conductivity of PANI in the composites at higher TEOS content.