Synthesis of silver nanoparticles coated with OH-functionalized organic groups: dispersion and covalent bonding in epoxy networks.

The introduction of reactive functionalities in the organic groups used to stabilize inorganic nanoparticles (NPs) enables multiple applications based on their covalent fixation to a variety of materials, substrates and interfaces. In this paper we report the synthesis of silver nanoparticles (NPs) with an average diameter of about 4 nm, coated with particular organic groups that allow their solubility in a variety of organic solvents and the covalent bonding through secondary hydroxyl groups present in their structure. Water-dispersible NPs stabilized with 11-mercaptoundecanoate anions were first synthesized. The esterification of carboxylate groups with phenyl glycidyl ether generated 2-hydroxyester functionalities and made the NPs dispersible in a variety of organic solvents. To illustrate the multiple possible applications of the synthesized NPs, their incorporation to an epoxy network is discussed. A solution of the silver NPs in diglycidyl ether of bisphenol A was polymerized in the presence of benzyldimethylamine as initiator. This led to an epoxy network containing a homogeneous dispersion of silver NPs as revealed by the constancy of the plasmon band location. Covalent bonding of the NPs to the epoxy matrix was produced by chain transfer reactions involving the hydroxyl groups. Nanocomposites were strongly colored and exhibited a dependence of the glass transition temperature on the concentration of NPs. Several applications are envisaged for these materials.