Formation of Nanoparticle-Loaded Microcapsules Based on Hydrogen-Bonded Multilayers

We show that hydrogen-bonded multilayer thin film coatings assembled on colloidal particles can be used as templates for the in situ synthesis of nanoparticles. The concentration and size of nanoparticles grown within the coatings can be tuned by the number of loading cycles. The hydrogen-bonded multilayer thin films were coated on polystyrene micrometer-sized colloidal particles and subsequently cross-linked via water-soluble carbodiimide chemistry. We show that metal nanoparticles (e.g., Ag and Pd) can be synthesized via the nanoreactor scheme, where corresponding metal ions are loaded into the coating and then subsequently reduced to create nanoparticles dispersed within the coating. In addition, we demonstrate the multiple loading capability of the hydrogen-bonded multilayer coatings. UV−vis spectroscopy and direct observation by transmission electron microscopy confirm that the nanoparticles are well-dispersed within the thin film coating. Finally, the polystyrene particles can be extracted by treating the nanocomposite-coated particles with tetrahydrofuran or toluene, leaving the nanoparticles embedded within the resultant multilayer hollow microcapsule walls.