Rapid fabrication of large-area nanoparticle monolayer films via water-induced interfacial assembly

Close-packed nanoparticle monolayer films have been assembled at the water/toluene interface, and they can be transferred onto various hydrophilic solid substrates. The method involves adding alcohol and then toluene (when the dispersant is itself alcohol, only toluene was added) into a hydrophilic nanoparticle dispersion, and then a large quantity of distilled water was rapidly poured into the mixed system. Simultaneously, nanoparticles in the dispersion were extracted to the water/toluene interface, forming a thin film with a metallic sheen. The close-packed structures of these thin films were verified by transmission electron microscopy (TEM) characterizations. This method can work well for those hydrophilic nanoparticles without strongly bonded stabilizers, such as citrate- stabilized Au nanoparticles, polyvinylpyrrolidone (PVP)-stabilized Pt or Ag nanoparticles, and SiO2 microspheres. Large-area nanoparticle monolayer films (e. g., more than 200 cm(2)) could be prepared in less than 10 s. Due to its inherent simplicity and speed, the method should be of significance for the nanofilm industry.