Electroless Deposition of Silver onto Silica Nanoparticles to Produce Lipophilic Core-Shell Nanoparticles

Hypothesis: The colloidal stability of noble metal nanoparticles can be tuned for solvents of varying hydrophobicity by modifying the surface chemistry of the particles with different capping agent architectures. Challenges arise when attempting to separately control multiple nanoparticle properties due to the interdependence of this adsorption process on the surface chemistry and metal architecture. A surfactant-mediated, templated synthesis strategy should decouple control over size and stability to produce lipophilic nanoparticles from aqueous reagents. Experiments: A modified electroless plating process that produces oil-dispersible core–shell silver-silica nanoparticles is presented. Amine-terminated alkanes are utilized as the capping agents to generate lipophilic surface coatings and the particles are temporarily stabilized during the synthesis by adding a Pluronic surfactant that enhances dispersibility in the aqueous reaction medium. The evolution of shell morphology, composition, and colloidal stability was analyzed against capping agent architecture and concentration. The role of particle shape was also tested by interchanging the template geometry. Findings: The capping agents installed on the silver shell surface displayed both colloidal stability enhancements and a minimum effective capping concentration that is a function of molecular weight without influencing the shell composition. Particle geometry can be controlled by interchanging the silica template size and shape.