vendredi 1er février 2013 à 11:00 en salle 120 du bâtiment 11E
Résumé : The spontaneous assembly of nanoparticles at fluid-fluid interfaces is exploited in a broad range of applications, including the fabrication of nanomaterials with tunable properties, and phase-transfer catalysis. Exquisite control over the microstructures formed by nanoparticles at fluid interfaces is an important goal in these contexts: the ability to reversibly tune the microstructure over a broad range of packing fractions, as well as to control nanoparticle removal and recovery, would be highly desirable. However, our understanding of the interactions of nanoparticles at interfaces and the resulting microstructures is still limited, due also to the important role played by grafted ligands in most nanoparticle systems. We studied gold nanoparticles capped with the amphiphilic ligand thioalkylated tetraethylene glycol, which spontaneously adsorb from aqueous suspension onto a pendant drop of oil. Using pendant drop tensiometry, we measured the surface pressure of the nanoparticle monolayer during adsorption and subsequent compression. In contrast to the commonly observed buckling of solid-like films of interfacial particles, upon compression the nanoparticles were mechanically forced out of the interface and back into suspension. Area density measurements by an optical absorbance method reveal that ligand-mediated short-range interparticle repulsion enables desorption upon compression. This finding points to new opportunities for engineering the dynamic response of nanoparticle monolayers by tuning interparticle interactions.
Valeria Garbin, Imperial College London