Résumé
Nano-ions (NIs) are ionic species or clusters of nanometric size.Their low charge density and the delocalization of their charges givespecial properties to some of NIs belonging to chemical classes ofpolyoxometalates (POMs) or boron clusters (BOCs). They have theparticularity of interacting non-covalently with neutral hydratedsurface or interfaces such as assemblies of surface-active molecules(micelles, vesicles, lyotropic liquid crystals), foam bubbles oremulsion droplets. This makes possible to classify those NIs in theHofmeister series as superchaotropic ions. The mechanism ofadsorption is complex, linked to the simultaneous dehydration of theion and the molecule or supramolecular assembly with which it caninteract, all with an enthalpic gain on the free energy of the system.This interaction process is reversible and is sufficiently pronounced toinduce changes in molecular and supramolecular shape orconformation, phase transitions in the liquid phase, all at sub-millimolar ionic concentrations. This new property of some NIs opensup new possibilities for applications in fields as varied as biochemistryfor solubilization, recovery of metals of interest by foams in the formof NIs... In order to better understand the physico-chemicalmechanisms at the origin of this interaction, we use silicon wafersfunctionalized by non-ionic oligomers (polyethylene glycol chains orPEG) to study in situ by X-ray reflectivity this interaction of NIs withthe grafted chains. A first study carried out at ESRF (EuropeanSynchrotron Radiation Facility) on BM32 and has shown that theadsorption of the NIs, such as POMs, characterized by a very stronginteraction at low concentrations. We aslo noticed this tendancy withBOCs on X-ray reflectivity lab set. Moreover the distribution of theNIs within the grafted PEG chain layer was quantify. These results arevery encouraging and confirm what has been observed on softinterfaces such as micelles or foams. The next step will be to explorea larger family of NIs. The possibility to play on the density, lengthand chemical nature of the grafted chains makes this system an idealtool to provide kinetic and thermodynamic information to decipher thecomplex mechanisms at the origin of this adsorption.