Preparation and characterization of magnetic polyaniline micropheres

Abstract

The Fe3O4 nanoparticles primarily prepared by precipitation-oxidation method, and the Fe3O4-PANI nanoparticles with core-shell structure is synthesized via an in-situ polymerization of aniline monomer in an aqueous solution, which contains well-dispersed Fe3O4 nanoparticles and surfactant NaBS. The particles are almost spherical with diameters ranging from 20~30 nm. These particles are polydisperse and some of them agglomerated due to magneto-dipole interactions between particles. TEM micrographs of Fe3O4-PANI nanoparticles, which is quite polydispersed. 70%~80% of the Fe3O4-PANI particles are ranged from 70~100 nm in diameter. In order to identify the core-shell structure of nanoparticles, the Fe3O4-PANI powder composite was dissolved with N-methyl-2-pyrrolidore, which is a good solvent for PANI, and observed by TEM again. The micrograph was similar to the micrograph of Fe3O4 particles. This result indicated Fe3O4-PANI nanoparticle was core-shell structure. The core is Fe3O4nanoparticles and the shell is composed of PANI. Fe3O4 content was found to affect significantly on both conductivity and magnetization of the resulting PANI composites. When 9% Fe3O4 was incorporated into PANI, the conductivity of PANI composite was greatly reduced from 5.55×10-3~1.53×10-4 s/cm. Further increasing of Fe3O4content from 16%~44%, results in slight reduction of the conductivity at room temperature. The decrease in conductivity of Fe3O4-PANI composite with increasing Fe3O4 content was due to a decrease in the doping degree, assigned as S/N ratio. The S/N ratios decrease from 0.31 to 0.09 with increasing Fe3O4 content from 0 to 44 %. The magnetic properties of the Fe3O4-PANI nanocomposite depend on the Fe3O4 content. Increasing Fe3O4 content from 0 to 44 considerably increases both the saturated magnetization (Ms) and the coercive force (Hc) from 0~55.4 emu/g and 0~62 Oe, respectively. Since PANI powder is not magnetic, the magnetic Fe3O4 nanoparticles are attributed to the ferromagnetic properties. The magnetic Fe3O4 nanoparticles can improve the thermal stability of Fe3O4-polyaniline nanocomposites due to interaction between Fe3O4 particles and polyaniline chains.