Formation of hybrid colloids by suspension polycondensation in the presence of hydrophilic block copolymers
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Formation of hybrid colloids by suspension polycondensation in the presence of hydrophilic block copolymers Corine GERARDIN1, 2, Valérie BUISSETTE2, François GAUDEMET2, Olivier ANTHONY2, Nicolas SANSON1, Francesco DIRENZO1, François FAJULA1. 1 Laboratoire de Matériaux Catalytiques et Catalyse en Chimie Organique, UMR 5618 CNRS ENSCM, 8, rue de l'Ecole Normale, 34296 Montpellier cedex 5, France. 2 CNRS Rhodia Complex Fluids Laboratory, Rhodia Inc., Cranbury, NJ 08512, USA. ABSTRACT Double hydrophilic block copolymers were used to control the growth of inorganic particles and directly prepare hybrid colloidal suspensions. Colloids of metal hydrous oxides were obtained by forced hydrolysis of metal ions in presence of the copolymers. The block copolymers contain a metal-complexing polyelectrolyte block and a stabilizing neutral block. The role of the first block is to ensure a controlled growth of the inorganic phase, while simultaneously, the second block ensures the colloidal stabilization. Phase diagrams presenting the conditions under which precipitation is inhibited are established. The nanoparticles are then characterized in terms of sizes, morphologies and surface charges. The main parameters controlling the size were identified : the copolymer-to-metal ratio and the metal prehydrolysis ratio. The synthesis steps were characterized. First, a key step of induced micellization of the hydrophilic copolymers leads to hybrid core-shell assemblies. The second step consists in mineralization of the micellar core. The suspension polycondensation leads to hairy particles whose morphologies depend on the nature of the metal and on synthesis parameters. INTRODUCTION The interest in finely dispersed particles of controlled composition, shape and size has considerably increased in recent years not only for fundamental reasons but also due to the various applications (catalysts, pigments, medicine…). The reason is that the relevant physical and chemical properties of nanoparticles depend not only on the chemical composition but also on their size and morphology. Much effort has then been focused on the development of new strategies for the synthesis of particles, with sizes in the region of a few nanometers to a few hundred nanometers. However, further improvements of these methods are required, especially regarding the control of the size on a wide range and the stability of suspensions towards addition of various compounds. This paper focuses on the synthesis of colloids of metal hydrous oxides. The most classical method to prepare such particles is homogeneous precipitation by hydrolysis of metal salts1, 2 ; the key parameters in the synthesis are the pH, the temperature, the nature of the counterions, the reactant concentrations, the aging time. Growth control can be achieved by the use of strong complexing agents such as citrate or oxalate ions. Polyelectrolytes can also be used as growth inhibitors. In any case, suspensions are not stable in the presence of increasing amounts of electrolytes. Hydrolysis methods to prepa
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