How Nano-Ions Act Like Ionic Surfactants


Max Hohenschutz, Isabelle Grillo, Olivier Diat, and Pierre Bauduin

[ Article ]

Recent studies have highlighted that nanometer-sized ions characterized by a low charge density have a strong propensity to adsorb to hydrated neutral surfaces or to bind to macrocyclic molecules cavities. This ion specific effect named “superchaotropicity” in reference to the more classical chaotropic behaviour, arises from a solvent mediated effect. New phase diagrams were investigated and small angle neutron scattering (SANS) experiments at ILL were performed (see Figure) in order to observe specifically the impact of nano-ions adsorption onto the surfactant self-assemblies and their interactions. Analysing the various data, we have shown that adding various salts of nano-ions to different mesophases of a non-ionic surfactant induces i) the disappearance of the liquid/liquid micellar diphasic regime versus T, ii) the spontaneous transformation of the cylindrical micelles in spherical ones and in strong repulsive interaction, iii) the spontaneous transformation of a swollen lyotropic lamellar phase into a vesicle phase. These effects are caused by the superchaotropicity of the nano-ions and measurable in the weak range of few micro-molar. Although similar effects were already observed by adding ionic surfactants, nano-ions have the particularity to dehydrate strongly the neutral surfactant assemblies and thus, charges screening action via adding more classical salts can generate new condensed structures.

Once again, many thanks to Isabelle’s investment in this project, a colleague we will never forget !


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