Résumé
When having low charge density, nanometer-sized ions, or nano-ions (NIs), strongly adsorb onto interfaces made of hydrated molecules, e.g. at micellar surface of carbohydrate or polyethylene glycols based surfactants.[1-3] They can also bind to macrocycles cavities, e.g. cyclodextrins.[4,5] These strong interaction of NIs with electrically neutral and polar systems is described as a “superchaotropic” behavior [1,4,6] in comparison with the more classical chaotropic and salting-in effect of smaller ions as iodide or thiocyanate but observed at much lower concentrations i.e the mM range.[7]Superchaotropic nano-ions were also shown recently to behave like ionic surfactants when added to non-ionic surfactant solutions.[8] Thus, we extended on this concept and have shown that the superchaotropic polyoxometalate Na4SiW12O40 (NaSiW) – and others- strongly stabilizes non-ionic surfactant foam similarly and even better than the ionic surfactant such as sodium dodecyl sulfate (SDS). Both DS- and SiW12O404- were incorporated into the foam films of Brij-O10, SiW12O404- by adsorbing within the polar non-ionic surfactant chain and SDS due to the hydrophobic effect with its aliphatic chain. However, SDS affects surface tension while NaSiW does not. Nevertheless, adding SDS or NaSiW to a Brij010 foam (0.5 mM) close to the equimolarity slow down liquid drainage and bubble Ostwald ripening as revealed by image analysis and conductivity measurements. Furthermore, as SiW12O404- adsorbs the non-ionic surfactant foam films they become charged, thicker and more stable, hindering film rupture as shown with Small Angle Neutron scattering. The high potential of superchaotropic nano-ions as foam stabilizers is herein discussed. [9]