PREPARATION AND CHARACTERIZATION OF PVA COATED MAGNETIC NANOPARTICLES*

 Polyvinyl alcohol coated magnetic particles (PVA ferrofluids) have been synthesized by chemical co-precipitationof Fe(Ⅱ)/Fe(Ⅲ) salts in 1.5 mol/L NH₄OH solution at 70℃ in the presence of PVA. The resultant colloidal particles havecore-shell structures, in which the iron oxide crystallites form the cores and PVA chains form the shells. The hydrodynamicdiameter of the colloidal particles is in the range of 108 to 155 nm, which increases with increasing PVA concentration from5 wt% to 20 wt%. The size of the magnetic cores is ca.5～10 nm,which is relatively independent of PVA concentration.Under transmission electron microscopic (TEM) examination,the magnetic cores exhibit somewhat irregular shapes varying from spherical,oval,to cubic.Magnetometry measurement revealed that the PVA coated magnetic particles are superparamagnetic.The saturation magnetization of 5 wt% and 20wt% PVA ferrofluids at 300 K is 54 and 49 emu/g,respectively.All the PVA ferrofluids exhibited excellent colloidal stability in pure water and phosphate buffer saline (PBS,pH=7.4).The ferrofluids can remain stable in above solutions for more than three months at 4℃.