(353g) Ion-Pair Interactions to Control the Assembly of Nanoparticles

We report on the ability on using ion-pair interactions to design monolayer protected clusters (MPCs) that spontaneously assemble at the liquid-liquid interface. First, our approach to use ion-pair association to dictate chain spacing in self-assembled monolayers (SAMs) will be detailed. Ion-pair directed assembly allows us to vary directly the coverage to create a film with surface properties (such as wetting, thickness, and electrochemical response) that depend on pH and applied potential. Control of molecular packing allows for the creation of responsive surfaces and mixed functionalities that are useful for sensing applications. Second, we will show, using infrared and X-ray spectroscopies that the ion-pairs remains as pairs during the synthesis of the nanoparticles, washing, and extraction of the nanoparticles. We also demonstrate that the surface coverage on the nanoparticles is the same as the one obtained for films on flat gold surfaces. Finally, we show that 7 nm nanoparticles covered with ion-pair monolayers spontaneously self-assemble and are stable at the toluene-water interface (with a contact angle of approx. 93o). We will also show that the particles can be easily transferred in the aqueous solution to obtain a stable dispersion of nanoparticles.