Electrokinetic Potential and Size Distribution of Magnetite Nanoparticles Stabilized by Poly(vinyl Pyrrolidone)

Abstract

The impact of different amounts of poly(vinyl pyrrolidone) (PVP) on the electrokinetic (ζ) potential and size distribution of magnetite particles, produced by co-precipitation method, in a wide pH interval (2–12) is studied. It has been shown that magnetite particles possess relatively high positive and negative ζ‑potentials (up to 40 mV) above and below the isoelectric point (IEP), respectively. The IEP of the sample corresponds to pH 6.6 which is shifted to pH 9.1 in 10^–2 M KCl solution. Addition of PVP shifts the IEP of the surface to higher pH values and substantially reduces the absolute value of the ζ-potential of both positively (in acidic media) and negatively (alkali media) charged particles as a result of formation of thick polymer layers on the surface. Adsorption of PVP gives a marked rise to the hydrodynamic diameter of magnetite particles but does not change the (monomodal) mode of their size distribution. Also it is shown that PVP can serve as an efficient stabilizer of magnetite particles in a broad pH interval. At the same time in the presence of high amounts (1–2 g PVP/g magnetite) of the polymer, and high pH values (10–11) the partial aggregation of particles takes place.