Role of double-hydrophilic block copolymers in the synthesis of lanthanum-based nanoparticles

The formation of nanosized lanthanum hydroxide particles in aqueous medium was studied in the presence of double-hydrophilic block copolymers (DHBC). These copolymers contain a polyacrylic acid (PAA) block as an ionizable block, and a polyacrylamide (PAM) or a polyhydroxyethylacrylate (PHEA) block as a neutral block. The nanoparticles are synthesized by a two-step procedure. Firstly, the complexation of lanthanum ions in water by the polyacrylate blocks induced the formation of star-shaped micelles stabilized by the PAM or PHEA blocks. The micelles were characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS) and transmission electron microscopy (TEM). Secondly, the inorganic polycondensation of lanthanum ions led to the formation of organic-inorganic nanohybrids. Hairy needle-like colloids were obtained. The size of the sterically stabilized colloids was controlled by adjusting the polymer-to-metal ratio. (C) 2002 Elsevier Science B.V. All rights reserved.