Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions.

Microgels are commonly applied as solute carriers, where the size, density, and functionality of the microgels depend on solute binding. As representatives for ionic solutes with high affinity for the microgel, we study here the effect of superchaotropic Keggin polyoxometalates (POMs) PWO (PW) and SiWO (SiW) on the aqueous swelling and internal structure of nonionic poly(-isopropylacrylamide) (pNiPAM) microgels by light scattering techniques and small-angle X-ray scattering. Due to their weak hydration, these POMs bind spontaneously to the microgels at millimolar concentrations.

When Ions Defy Electrostatics: The Case of Superchaotropic Nanoion Adsorption.

Nanometer-sized anions, like polyoxometalates and borate clusters, bind to nonionic hydrated matter driven by the chaotropic effect, which arises from the favorable dehydration of the ions. Herein, we evaluate the adsorption and activity coefficient of the superchaotropic Keggin polyoxometalate SiWO (SiW) on nonionic surfactant (CE) micelles by modeling small-angle X-ray and neutron-scattering spectra. Neither hard sphere nor electrostatic repulsion models reproduce the experimental activity coefficient of adsorbed SiW ions on the micelles.

Repulsive, but sticky - Insights into the non-ionic foam stabilization mechanism by superchaotropic nano-ions.

Hypothesis: The superchaotropic Keggin polyoxometalate α-SiWO (SiW) was recently shown to stabilize non-ionic surfactant (CE) foams owing to electrostatic repulsion that arises from the adsorption of SiW-ions to the foam interfaces. The precise mechanism of foam stabilization by SiW however remained unsolved.

Experiments: Imaging and conductimetry were used on macroscopic foams to monitor the foam collapse under free drainage and small angle neutron scattering (SANS) at a given foam height allowed for the tracking of the evolution of film thickness under quasi-stationary conditions.

Superchaotropic Nano-ion Binding as a Gelation Motif in Cellulose Ether Solutions.

Nanometer-sized anions (nano-ions) like polyoxometalates and boron clusters exhibit so-called superchaotropic behavior, which describes their strong binding to hydrated non-ionic matter in water. We show here that nano-ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non-ionic cellulose ethers (CEs), a class of widely utilized polymers known for their thickening and gel-forming ability. These phenomena arise from an interplay of attractive forces and repulsive electrostatic forces between CE-chains upon nano-ion binding.

Superchaotropic nano-ions as foam stabilizers.

Hypothesis: Weakly hydrated nanometric ions, called superchaotropes, were recently shown to adsorb strongly to non-ionic surfaces affecting drastically the surface's physical-chemical properties due to a charging effect. Superchaotropic ions could serve as stabilizing agents for non-ionic colloidal systems, such as non-ionic surfactant foams.

Experiments: We study foams of the non-ionic surfactant BrijO10 (CE) without and in presence of the superchaotropic Keggin-ion SiWO (SiW).

How Nano-Ions Act Like Ionic Surfactants.

Recently, nanometric ions were shown to adsorb to hydrated neutral surfaces and to bind to the cavities of macrocyclic molecules with an unexpectedly strong affinity arising from a solvent-mediated effect named superchaotropicity. We show here that nano-ions at low concentrations (μm range), similarly to anionic surfactants, induce the spontaneous transformation of a swollen lyotropic lamellar phase of non-ionic surfactant into a vesicle phase. This transition occurs when the neutral lamellae acquire charges, either by adsorption of the nano-ions onto, or by anchoring of the ionic surfactant into the lamellae.