Infrared external reflection spectra of Janus gold nanoparticle monolayers prepared at the air-water interface

Nanoparticle monolayers at the air-water interface have received broad attention because of their potential applications owing to the tunability of their surface properties. We prepared gold nanoparticle monolayers by adsorption of hydrophilized nanoparticles from solution onto Langmuir monolayers of amphiphilic organic molecules (polyion complexes of deuterated stearic acid and polyallylamine) at the air-water interface, followed by adsorption of dodecyltrimethylammonium bromide onto the underside of these particles. The infrared external reflection spectra of the monolayers recorded both during and after preparation showed that the adsorption of gold nanoparticles on the Langmuir monolayers and that of dodecyltrimethylammonium bromide on the nanoparticles occurred in several tens of minutes. The infrared spectra also showed that both stearic acid and dodecyltrimethylammonium bromide molecules were highly ordered on the gold nanoparticles at the air-water interface. These results suggested that this preparation procedure is a useful fabrication method for Janus particles.