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The self-assembly of organic amphiphilic species into various aggregates such as spherical or elongated micelles and cylinders up to the formation of lyotropic hexagonal or lamellar phases results from cooperative processes orchestrated by the hydrophobic effect, while those involving ionic inorganic polynuclear entities and nonionic organic components are still intriguing. Herein, we report on the supramolecular behavior of giant toroidal molybdenum blue-type polyoxometalate, namely, the {Mo154} species in the presence of n-octyl-β-glucoside (C8G1), widely used as a surfactant in biochemistry. Structural investigations were carried out using a set of complementary multiscale methods including single-crystal X-ray diffraction analysis supported by molecular modeling, small-angle X-ray scattering and cryo-TEM observations. In addition, liquid NMR, viscosimetry, surface tension measurement, and isothermal titration calorimetry provided further information to decipher the complex aggregation pathway. Elucidation of the assembly process reveals a rich scenario where the presence of the large {Mo154} anion disrupts the self-assembly of the C8G1, well-known to produce micelles, and induces striking successive phase transitions from fluid-to-gel and from gel-to-fluid. Herein, intimate organic–inorganic primary interactions arising from the superchaotropic nature of the {Mo154} lead to versatile nanoscopic hybrid C8G1–{Mo154} aggregates including crystalline discrete assemblies, smectic lamellar liquid crystals, and large uni- or multilamellar vesicles where the large torus {Mo154} acts a trans-membrane component.

Understanding clay flotation mechanisms has become a major concern because of the increasing level of environmental contamination of soil and ground water by heavy metals and radionuclides. Clays are often used as sorbents for extracting metals in indirect flotation processes but can function simultaneously as defoamers. However, how foam generation and stability depend on the molecular interactions between the clays and surfactant is still controversial. In the present study, an amine polyethoxylated surfactant was used as a bifunctional surfactant that collected clay particles and acted as a foaming agent in the flotation process. The pH conditions strongly affected the surfactant physicochemical properties, allowing the clay extraction efficiency to be tuned. The interfacial recovery factor of the clays almost reached 100% under acidic (pH < 6) and neutral (pH 6–10) conditions, whereas it was negative under alkaline conditions (pH > 10), contrary to expectations. To elucidate the mechanisms involved in the particle flotation process for each of the pH conditions, the bulk and foam phases were analyzed. The effects of electrostatic interactions between the solutes and multiscale structure on the clay extraction behavior were investigated by electrophoretic measurements, dynamic light scattering, small-angle neutron scattering, and image analysis. Based on these results, three flotation processes were found depending on pH range: surfactant foam fractionation at pH > 10; clay particle foam flotation at pH 6–10; and particle froth flotation at pH < 6.

We show here for the first time that short chain poly(N-isopropylacrylamide) (PNIPAM), one of the most famous thermoresponsive polymers, self-assembles in water to form (i) discrete nanometer-globules and (ii) micrometric sheets with nm-thickness upon addition of the well-known Keggin-type polyoxometalate (POM) H3PW12O40(PW). The type of self-assembly is controlled by PW concentration: at low PW concentrations, PW adsorbs on PNIPAM chains to form globules consisting of homogeneously distributed PWs in PNIPAM droplets of several nm in size. Upon further addition of PW, a phase transition from globules to micrometric sheets is observed for PNIPAMs above a polymer critical chain length, between 18 and 44 repeating units. The thickness of the sheets is controlled by the PNIPAM chain length, here from 44 to 88 repeating units. The PNIPAM sheets are electrostatically stabilized PWs accumulated on each side of the sheets. The shortest PNIPAM chain with 18 repeating units produces PNIPAM/PW globules with 5–20 nm size but no sheets. The PW/PNIPAM self-assembly arises from a solvent mediated mechanism associated with the partial dehydration of PW and of the PNIPAM, which is related to the general propensity of POMs to adsorb on neutral hydrated surfaces. This effect, known as superchaotropy, is further highlighted by the significant increase in the lower critical solubilization temperature (LCST) of PNIPAM observed upon the addition of PW in the mM range. The influence of the POM nature on the self-assembly of PNIPAM was also investigated by using H4SiW12O40(SiW) and H3PMo12O40(PMo), i.e. changing the POM’s charge density or polarizability in order to get deeper understanding on the role of electrostatics and polarizability in the PNIPAM self-assembly process. We show here that the superchaotropic behavior of POMs with PNIPAM polymers enables the formation and the shape control of supramolecular organic–inorganic hybrids.

Ion extraction processes show some limitations related to their selectivity, efficiency, cost and ecological footprint. The recent Fukushima event has stimulated the hunt for innovative extraction processes of the caesium ion. Here, we propose a caesium foam flotation process of a highly selective complexing agent, namely the copper based Prussian blue analogue (Cu-PBA), using a pH-sensitive foaming agent (collector): a polyethoxylated amine surfactant (Ethomeen®). The foaming properties, surface charge and surface activity of this complex chemical system have been investigated as a function of pH. It was demonstrated that the pH controls the flotation efficiency through electrostatic interactions between the surfactant and the Cu-PBA. The flotation was highly efficient for pH < 5, where all of the Cu-PBA was extracted by the foam. In contrast, for pH > 10, all of the Cu-BPA remained in the foaming solution and was not extracted in the foam. As a consequence, reversible extraction/de-extraction of the Cu-PBA was made possible through pH cycles, which enables the recycling of the surfactant, reducing both the cost and the environmental impact of the overall process.

Polyoxometalates (POMs) are nanometric metal–oxide anions with unique chemical and physical properties. During the past decade, significant efforts have been made to give POMs surface activity and self-assembly properties that are essential for catalysis applications and for producing organic–inorganic hybrid materials. In this work, POMs-based surfactants are produced spontaneously through noncovalent interactions in water by mixing nonionic surfactants with POM. The most common POMs of tungstosilicate and tungstophosphate have indeed an unexpected strong tendency to adsorb on polar and neutral interfaces. Micelles in water and water/air interfaces were investigated by SAXS and ion flotation showing the POM anions adsorbed at the micelle surface and on monolayers of nonionic surfactants. This general property of POM provides a unique opportunity for deeper understanding of many medicinal effects of POMs, i.e., their antiviral and antitumor activities that involve their specific adsorption on biological surfaces.

A review of the four microstructures present in oil phases of malonamide extractants used for nuclear fuel reprocessing is presented in relation with the extraction properties and the third phase formation. Due to their surface active properties, extractants can be considered as a weak surfactants and are organised into reverse micelles interacting through an attractive potential. The Van der Waals attractions between the cores of reverse micelles are the key parameters for understanding “third phase” formation. Extractant solutions are similar to reverse microemulsions and the stability rules known in the field of microemulsions can be applied. In some cases, micelles are transformed into a regular molecular solution by modest heating. Apart from micellar and regular solutions, two new modes of association of extractant molecules have been identified. Networks of H-bounds are obtained when “modifiers” such as octanol are added by formulators in order to improve stability range. Microphase separation in a more crystalline phase may be obtained by increasing extractant and/or ion concentrations.

The synthesis of short eco-friendly amphiphilic compounds derived from glycerol was carried out. These compounds, called solvo-surfactants, are of great interest since they exhibit both properties of solvents, e.g.volatility, solubilization of organics, and surfactants, e.g.reduction of interfacial tensions, formation of emulsions and microemulsions. Their surface activity was studied, and binary phase diagrams with water were drawn. Their sensitivity to various electrolytes from Hofmeister's series was also investigated. Short chain glycerol 1-monoethers constitute a new class of green solvo-surfactants with excellent properties, that should be seriously considered for the replacement of reprotoxic glycol ethers. They have, moreover, the advantage of helping to solve the problem of an over-production of glycerol, which is a major side-product of the biocarburant industry.

The influence of different salts on the lower critical solution temperature (LCST) of mixtures of propylene glycol propyl ether and of dipropylene glycol propyl ether with water was determined experimentally. It was observed that the temperature shifts follow precisely the same Hofmeister series for anions that was originally found for salting-in and salting-out effects for protein solutions. The results are similar to the observations found for mixtures of water with non-ionic surfactants. In the case of dipropylene glycol propyl ether mixtures with water, temperature dependent phase diagrams in the presence of one salting-in (NaSCN) and one salting-out (Na2SO4) salt were measured at a fixed salt concentration in water of 0.041 M. The results can be qualitatively understood by assuming a different hydrophobicity for both types of salts. They further hint at a strong degree of solute determined cooperative water structure.

Sandwiched: The cobaltabisdicarbollide (mono‐)anion ([3,3′‐Co(1,2‐C2B9H11)2]−, COSAN−) forms monolayer vesicles at low concentrations in water (see picture). An increase in concentration leads to a Coulomb explosion of the closely packed vesicles into small micelles, which results in the coexistence of both aggregation states at higher concentrations.

Als Sandwich serviert: Das Cobaltabisdicarbollid (Mono‐)Anion ([3,3′‐Co(1,2‐C2B9H11)2]−, COSAN−) bildet bei niedrigen Konzentrationen in Wasser aus Monoschichten bestehende Vesikel (siehe Bild). Eine Erhöhung der Konzentration führt zu einer Coulomb‐Explosion der dicht gepackten Vesikel in kleinere Micellen. Dadurch koexistieren beide Aggregate bei höheren Konzentrationen.

The theta‐shaped amphiphilic structuretogether with the charge density and rigidity of the cobaltabisdicarbollide (mono‐)anion ([3,3′‐Co(1,2‐C2B9H11)2]−, COSAN−) lead to an unconventional aggregation behavior. In their Communication on page 5298 ff.,P. Bauduin and co‐workers describe the concentration‐dependent formation of both vesicles and micelles in water.

Die Theta‐förmige amphiphile Struktursowie die Ladungsdichte und die Formtreue des Cobaltabisdicarbollid‐Anions ([3,3′‐Co(1,2‐C2B9H11)2]−, COSAN−) führen zu einem ungewöhnlichen Aggregationsverhalten. In ihrer Zuschrift auf S. 5410 ff.beschreiben P. Bauduin et al. die konzentrationsabhängige Bildung von sowohl Vesikeln als auch Micellen in Wasser.