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The monoammonium salt of glycyrrhizic acid (AGA) is known to form fibrillar hydrogels and few studies regarding self-assembly of AGA have been published. Yet, the understanding of the fibrillar microstructures and the gelation remains vague. Thus, we attempt to achieve a deeper understanding of the microstructures and the gelation process of binary solutions of AGA in water. Further, we examine the effect of ethanol on the microstructures to pave the way for potential enhancement of drug loading in AGA hydrogels.A partial room temperature phase map of the ternary system AGA/ethanol/water was recorded. Small-angle X-ray and neutron scattering experiments were performed over wide ranges of compositions in both binary AGA/water and ternary AGA/ethanol/water mixtures to get access to the micro-structuring.Binary aqueous solutions of AGA form birefringent gels consisting of a network of long helical fibrils. 'Infinitely' long negatively charged fibrils are in equilibrium with shorter fibrils (≈25 nm), both of which have a diameter of about 3 nm and are made of around 30 stacks of AGA per helical period (≈9nm), with each stack consisting of two AGA molecules. The interaxial distance (order of magnitude ≈20 nm) varies with an almost two-dimensional swelling law. Addition of ethanol reduces electrostatic repulsion and favors the formation of fibrillar end caps, reducing the average length of shorter fibrils, as well as the formation of small, swollen aggregates. While the gel network built by the long fibrils is resilient to a significant amount of ethanol, all fibrils are finally dissolved into small aggregates above a certain threshold concentration of ethanol (≈30 wt%).

The characterization of nanoporous powders of highly absorbing compounds by small-angle X-ray scattering (SAXS) involves overcoming several difficulties before quantitative information related to the porous texture, such as the specific surface and the porous volume, can be derived. In this article, first, the contribution of the grain facet reflectivity and scattering from the bulk of a grain with the density of ThO2, a highly absorbing material, were calculated. Microporous ThO2 powder having micrometric grain size was characterized, in which the scattering signal is predominant. A high-resolution synchrotron instrument was used in order to cover a wider q range and minimize the absorption effect, and the results were compared with those obtained using a laboratory X-ray source. Concerning the absorption problem existing with a laboratory X-ray source, a new and robust experimental method was proposed to correctly determine the scattering intensity of the highly absorbing granular samples on an absolute scale. This method allows one to calculate accurately the porous volume and the specific surface via Porod's law and the invariant using a laboratory SAXS instrument. This last result opens new perspectives for the characterization of the volume and the specific surface of highly absorbing actinide oxide powders.

In a recent paper, we determined the phase behavior of an aqueous solution of octyl ether octaethylene oxide carboxylic acid ([HWe established the respective phase diagrams of the above-mentioned salts in water and determined the structures of the occurring phases in detail with small-and wide-angle X-ray scattering, small-angle neutron scattering, dynamic light scattering, heat flux differential scanning calorimetry, as well as surface tension, ESI-MS, and NMR experiments.To our surprise, we discovered a new type of nematic phase between an isotropic and a hexagonal phase. Based on the complete description of all occurring phases both in the acidic and the charged surfactant systems, we were able to design a coherent and unified picture of all these phases, including the auto-coacervation at low surfactant concentration, the non-conventional clouding at high temperatures, the unusual liquid crystalline phases in a small domain at high surfactant concentrations, and the L

Water-ethyl acetate-ethanol is widely used as “green” extractant system. We show that two different types of phase separation can be induced upon centrifugation in this ternary system using ethanol as a co-solvent of water and ethyl acetate (EA): centrifuge-induced criticality and centrifuge-induced emulsification. The expected composition profiles of samples after centrifugation can be represented by bent lines in a ternary phase diagram when gravitational energy is added to the free energy of mixing. The experimental equilibrium composition profiles behave qualitatively as expected and can be predicted using a phenomenological theory of mixing. The concentration gradients are small except near the critical point, as expected for small molecules. Nevertheless, they are usable when accompanied by temperature cycles. These findings open new possibilities of centrifugal separation, even if control is delicate during temperature cycles. These schemes are accessible even at relatively low centrifugation speed for molecules that float and sediment with apparent molar masses several hundred times larger than the molecular mass.

International audience; We use the model system ethanol–dodecane to demonstrate that giant critical fluctuations induced by easily accessible weak centrifugal fields as low as 2000g can be observed above the miscibility gap of a binary liquid mixture. Moreover, several degrees above the phase transition, i.e. in the one-phase region, strong gradients of ethanol concentration occur upon centrifugation. In this case, the standard interpretation of sedimentation equilibrium in the analytical ultracentrifuge (AUC) yields an apparent molar mass of ethanol three orders of magnitude higher than the real value. Notably, these composition gradients have no influence on the distribution gradient of solutes such as dyes like Nile red. The thick opaque interphase formed upon centrifugation does not appear as the commonly observed sharp meniscus, but as a turbidity zone, similar to critical opalescence. This layer is a few millimeters thick and separates two fluids with low compositional gradients. All these effects can be qualitatively understood and explained using the Flory–Huggins solution model coupled to classical density functional theory (DFT). In this domain hetero-phase fluctuations can be triggered by gravity even far from the critical point. Taking into account Jean Perrin's approach to external fields in colloids, a self-consistent definition of the Flory effective volume and an explicit calculation of the total free energy per unit volume is possible.

International audience; Amine-based extraction processes are broadly exploited for the selective extraction of uranium from sulfuric leaching liquors. The molecular forces (that is, the enthalpy associated with the multi-scale structuration of tertiary amines) are balanced by entropic effects that have not yet been identified. This first part in a series of reports describes the effects of the alkyl chain configuration on the phase stability and aggregation properties of tertiary amines. It is demonstrated that tertiary amines with longer or slightly branched alkyl chains provide better phase stability and enable constant extraction of uranium. In comparison, more branching of the alkyl chains hinders the formation of a highly curved interfacial layer, thus preventing efficient extraction. Combined small-angle scattering determination of the nanostructures in the organic phase and oil–water surface tension measurements revealed that the alkyl chains effects on the efficiency of the extraction process and phase stability are associated with reverse aggregates with smaller polar core volumes and less co-extracted water, suggesting that packing of the alkyl chains has a direct impact on the extraction efficiency of the solvent extraction system.

International audience; In solvent extraction, the self-assembly of amphiphilic molecules into an organized structure is the phenomenon responsible for the transfer of the metal ion from the aqueous phase to the organic solvent. Despite their significance for chemical engineering and separation science, the forces driving the solute transfer are not fully understood. Instead of assuming the simple complexation reaction with predefined stoichiometry, we model synergistic extraction systems by a colloidal approach that explicitly takes into account the self-assembly resulting from the amphiphilic nature of the extractants. Contrary to the current paradigm of simple stoichiometry behind liquid–liquid extraction, there is a severe polydispersity of aggregates completely different in compositions, but similar in the free energy. This variety of structures on the nanoscale is responsible for the synergistic transfer of ions to the organic phase. Synergy can be understood as a reciprocal effect of chelation: it enhances extraction because it increases the configurational entropy of an extracted ion. The global overview of the complex nature of a synergistic mixture shows different regimes in self-assembly, and thus in the extraction efficiency, which can be tuned with respect to the green chemistry aspect.

Microemulsions, as thermodynamically stable mixtures of oil, water, and surfactant, are known and have been studied for more than 70 years. However, even today there are still quite a number of unclear aspects, and more recent research work has modified and extended our picture. This review gives a short overview of how the understanding of microemulsions has developed, the current view on their properties and structural features, and in particular, how they are related to applications. We also discuss more recent developments regarding nonclassical microemulsions such as surfactant-free (ultraflexible) microemulsions or ones containing uncommon solvents or amphiphiles (like antagonistic salts). These new findings challenge to some extent our previous understanding of microemulsions, which therefore has to be extended to look at the different types of microemulsions in a unified way. In particular, the flexibility of the amphiphilic film is the key property to classify different microemulsion types and their properties in this review. Such a classification of microemulsions requires a thorough determination of their structural properties, and therefore, the experimental methods to determine microemulsion structure and dynamics are reviewed briefly, with a particular emphasis on recent developments in the field of direct imaging by means of electron microscopy. Based on this classification of microemulsions, we then discuss their applications, where the application demands have to be met by the properties of the microemulsion, which in turn are controlled by the flexibility of their amphiphilic interface. Another frequently important aspect for applications is the control of the rheological properties. Normally, microemulsions are low viscous and therefore enhancing viscosity has to be achieved by either having high concentrations (often not wished for) or additives, which do not significantly interfere with the microemulsion. Accordingly, this review gives a comprehensive account of the properties of microemulsions, including most recent developments and bringing them together from a united viewpoint, with an emphasis on how this affects the way of formulating microemulsions for a given application with desired properties., T.Z. thanks the German Science Foundation (DFG) for providing a Mercator professorship within the International Research Training Group (IRTG) 1524 (SSNI) at the Technische Universität Berlin, as well as the Agence Nationale de la Recherche (ANR) for the LABEX “Chemisyst” grant ANR 2011-01-05 that made the long-term collaboration possible.

Solubility, extraction and stabilization of curcumin extracted from Curcuma longa are still a challenge. Either the solubility power of the extracting solvent mixture is not at its optimum or non-sustainable solvents are used or the curcumin instability against oxidation is a problem. In order to tackle these problems, we consider here a promising alternative solvent medium, which is a ternary system composed of water/sodium salicylate (an anionic, preservative hydrotrope)/ethyl acetate. The effects of the structuring of the system are also studied. The position of the new critical point and the orientation of tie-lines in the liquid/liquid area were determined and further examined via interfacial tension and diffusion ordered spectroscopy (DOSY NMR) measurements. The critical point between the mono-phasic region and the liquid/liquid area is a classical one, around which no special nano-structuring is found, in contrast to some other ternary mixtures with hydrotropes. The system was investigated in terms of its curcumin solubility and its extraction power thereof. Good extraction yields (~90% of the Soxhlet reference) could be achieved in the area of best solubility. Surprisingly, the hydrophobic curcumin shows a significant solubility in systems that contain a significant amount of water in presence of sodium salicylate. These mixtures are far from the critical point but show significant structuring. The solubility is even higher than in pure ethyl acetate. At the point of highest solubility (water/sodium salicylate/ethyl acetate 7/13/80 w/w/w) 15.48 mg of curcuminoids per g Curcuma longa are successfully extracted. The partition coefficient in the lower liquid/liquid two-phasic region was determined for a subsequent purification of curcumin by precipitation. Surprisingly, curcumin accumulates at the “oil-water” interface in the more polar phase. Sodium salicylate could be removed from the precipitated curcumin by washing it with water (no trace of sodium salicylate has been detected with NMR after the washing process). The preservative effect of salicylate against the oxidative effect of light on curcumin was found to be significant. A better stabilization of curcumin was observed far away from the critical point and was most efficient in the region, where aggregates could be detected. So, extraction, solubilization, and chemical stabilization of a light sensitive substance could be performed using an anti-oxidative hydrotrope.

Hypothesis The surfactant C8EO8CH2COOH (Akypo LF2) and its salts have a small hydrophobic and a significantly longer hydrophilic part. As a consequence, there must be a significant steric constraint, once these surfactant molecules form micelles. In addition, the partially charged headgroups should bring some additional fine-tuning via electrostatic interactions to this “essentially non-ionic” surfactant. Experiments Phase diagrams of binary mixtures of water and C8EO8CH2COOH are established over large concentration and temperature ranges, also at different pHs and in the presence of sodium and calcium ions. Surface tensions and osmotic pressures are measured to understand the systems. To evaluate the microstructures, also Dynamic Light Scattering and Small-Angle X-ray Scattering are performed. Findings Apart from the formation of coacervates at very low surfactant concentrations, spherical micelles persist over the whole concentration and temperature range and do not change in size and shape. At very high surfactant concentrations, above 60% by weight, where the headgroups are no longer fully hydrated, the standard core-shell structure of micelles vanishes and highly stabilized aggregates of 8–26 octyl chains are suspended in interdigitated polyoxyethylene layers and form an “osmotic brush”. When the acid is partially transformed to a sodium salt, the repulsion between the micelles increases, whereas bridging between micelles prevails, when the counterions are calcium cations. Remarkably, the negative charges of the headgroups are randomly distributed in the hydrophilic ethylene oxide shell. Altogether, a phase diagram without lyotropic liquid crystalline phases and an extreme shift of the cloud-point in temperature and composition is found, similar to the phase diagram of C8EO8OH already known in literature. The phase properties can be explained by the curvature and packing constraints together with the Lindemann rule applied to short hydrocarbon chains.

International audience; Producing compact monoliths of mesoporous uranium oxide that are free from surface active components and able to be wet by highly radioactive solutions is of great interest for future nuclear technologies. In this direction, metastable colloidal sols of UO2 using U(IV) as precursor and carboxylic surfactants (Polyoxyethylene(9) oleyl ether carboxylic acid C16/18:1E9COOH and Polyoxyethylene(10) lauryl ether carboxylic acid C12E10COOH) have been successfully prepared by indirect precipitation for 6 pH 8 with a molar ratio between uranium and surfactant U/S

International audience; Surfactant film rigidity is a ubiquitous general concept that is quantified in two different units. We show here how to convert the bending rigidity from reduced units of a virtual infinitely thin film (not made of molecules) into the chemical unit (kJ.mol-1) of a realistic film of monomolecular thickness. In most cases molecular lengths are not negligible versus curvature radius. Two bending constants for the elasticity of thin-shelled solids can be defined, as introduced by Gauss, whereas only one physical bending constant taking into account that the film cannot be teared has been introduced in the nineties by Hyde and Ninham. The explicit conversion depends on the topology and is different in the quasi-planar approximation, as well as the “direct” o/w or “reverse” w/o case of spherical or cylindrical micelles. We show some examples for classical and nonclassical micelles and microemulsions of different topologies in (H,N coordinates).

International audience; We consider a structural and thermodynamic analysis of uranium solvent extraction by tertiary amines for which the alkyl chain configuration has been modified. The first part of this work revealed that tertiary amines with longer or branched alkyl chains allow tuning the phase stability and uranium extraction by modifying the volume of the polar species extracted in the organic phase. A complete fit of SANS data confirms in this second part that this phenomenon is related to the supramolecular self-assembly of the tertiary amines into smaller reverse micelle like aggregates for longer or branched alkyl chains. It moreover shows that these smaller aggregates quench third phase formation thanks to reduced attractive interactions between them. A thermodynamic analysis based on the “ienaic” approach further rationalizes this effect by showing that alkyl chains have a significant effect on the aggregate’s curvature free energy. The latter becomes a predominant inhibitor of uranium free energy of transfer due to the high entropic contribution originated by the extractants branching and packing.

Solvent-based liquid-liquid extraction and stripping is the key separation method at the basis of all hydrometallurgical processes, such as those used to retrieve strategic metals from ores or waste material. During formulation of an efficient extraction system, chemical engineers often encounter instabilities and the formation of undesired phases. In order to avoid the appearance of those in practice, we propose a simple and convenient approach of the phase diagram, based on mole ratio of cations as the variable that controls interfacial curvature. The proposed formulator’s cut through the Gibbs phase prism is more adapted than fish-cuts or similar ones in the case of extraction and stripping formulation optimized against variation in the feed composition.

International audience; We develop a minimal model of weak aggregation in water in the case of neutral extractant in a Winsor II regime, i.e. dispersed microemulsions in thermodynamic equilibrium with concentrated brine. All the terms involved in the free energy associated with the transfer of ions from a concentrated aqueous to an organised organic phase have been estimated: supramolecular effects, bulk terms, extractant film bending and electric polarisation terms. This allows the rationalization of the paradoxical observation of apparent stoichiometry: “constant” associated with the phase transfer that varies with the nature of the solvent and the bending properties of the surfactant. The extractant film is characterized by its spontaneous packing parameter (of the order of 4) and its intrinsic rigidity of the order of 6.25 kJ mol$^{−1}$ (2.5 $k_BT$). This multi-scale study combining supramolecular chemistry and mesoscale modelling approach allows a large reduction of the number of parallel apparent equilibria currently used for dimensioning extraction devices. Prediction power versus variations of water activity and temperature is in reasonable agreement with observations made in typical pilot cascade

The influence of the corrosion on the evaporation of sessile droplet of sodium chloride solution was quantitatively investigated at a relative humidity of 0%. On planar surface, sessile saline droplets evaporated in the pinned, constant contact area mode. The time of evaporation of a sessile saline droplet is much longer on iron substrate than on silicon. This is due to the initiation of corrosion phenomenon. At low and intermediate salt concentrations, the inverse of the classical Evans model is observed due to the evaporation time which is fast and the hydrodynamic flows linked to evaporation. Increasing salt concentration leads to the same evaporation rate for iron and silicon. This study shows that the conditions of evaporation will influence both the evaporation itself and the corrosion phenomenon.

The viscosity increase of the organic phase when liquid–liquid extraction processes are intensified causes difficulties for hydrometallurgical processes on industrial scale. In this work, we have analyzed this problem for the example of N,N-dialkylamides in the presence of uranyl nitrate experimentally. Furthermore, we present a minimal model at nanoscale that allows rationalizing the experimental phenomena by connecting the molecular, mesoscopic and macroscopic scale and that allows predicting qualitative trends in viscosity. This model opens broad possibilities in optimizing constraints and is a further step towards knowledge-based formulation of extracting microemulsions formed by microstructures with low connectivity, even at high load with heavy metals.

International audience; Industrial-scale rare earth extraction is typically performed by liquid-liquid extraction with large amounts of solvents, acids and organophosphorus ligands. An alternative is to use these extractants in supercritical CO$_2$ (SC-CO$_2$), where the crucial operating parameter is their solubility. Different molecules with amidophosphonate backbones have been synthesized and investigated in view of improving their solubility in SC-CO$_2$ and thereby their cerium extraction capacity. The CO$_2$-philicity of these extractants was adjusted by attaching branched or linear alkyl chains with four, six and eight carbons. Using a dynamic gravimetric setup, the solubility and cerium extraction capacity of these molecules were measured to vary from 1.56 to 2.47 mmol$_{ligand}$.mol$_{CO2}$$^{-1}$ and 0.25 to 0.46 mmol$_{Ce}$.mol$_{ligand}$$^{-1}$, respectively.The two properties were correlated and in both cases the highest values were obtained with a diisobutylamine chain. Solubility measurements between 313 and 331 K and between 13 and 28 MPa shows that optimal condition is (320 K ; 28 MPa).

International audience; Porous media in extraction and especially pertraction are often suspected to add unnecessary diffusive resistance and considerably slow down extraction kinetics. This work presents a miniaturized pertraction device and simulation of diffusive and reactive solute transport. Kinetics are experimentally observed and numerically fitted. Reaction rates – or solute transfer rates – are estimated via this fit on a numerical basis. The work shows that the diffusive resistance created by a porous medium is prevalent only at low distribution coefficients. At high distribution coefficients as is the case of quasi all industrial processes, the porous membrane does not interfere with overall kinetics. Instead, the diffusive resistance is shared between the feed and extraction phases, and the interface transfer, depending on the value of the transfer rate. Overall, this work can be generalize as enabling the measurement of solute transfer rates at the liquid-liquid interface, a key parameter in pertraction and membrane separation which is difficult to measure using classic methods of extraction.

Understanding and Prediction of the Clouding Phenomenon by Spontaneous and Effective Packing Concepts. N2 - In this work, we show by which mechanism branching of the hydrocarbon chains influences the cloud point of nonionic, ethoxylated surfactants. The temp.-induced sepn. into a dil. and a concd. liq. phase is of liq.-gas type and can be explained by the relative probability of endcaps and branching points of the cylindrical micelles in both phases. The influence of branches on the hydrocarbon chains can be easily understood by means of spontaneous and effective packing concepts, while quantification via hydrophilic/lipophilic balance (HLB), hydrophilic-lipophilic difference (HLD), and HLD-Net Av. Curvature requires parametrization. The phase equil. above the cloud point phenomenon is equiv. to the Winsor I type phase equil., one of the five known phase equil. in ternary systems.

Small amounts of nonpolar additives can have a tremendous impact on viscosity and viscoelasticity of giant micelles and completely change macroscopic properties. The effect can be best understood with the establishment of complete salt curves by screening surfactant viscosity as a function of electrolyte concentration. From previous studies in micellar systems of sodium laureth sulfate (SLES) with fragrance molecules, two independent mechanisms could be identified, co-solvent type interactions leading to a decrease of the maximum viscosity, and co-surfactant type interactions that cause the salt curve shift to the left. Our studies here reveal two new mechanisms with different effects on the salt curve. In particular, with long-chain hydrocarbons from n-octane to n-tetradecane a right shift was observed, whereas with short-chain or cyclic hydrocarbons such as n-hexane or cyclohexane the maximum viscosity increases. The two effects are interpreted via an extension of a recently developed thermodynamic model where changes in viscosity can be rationalized by a rebalance of the relative concentration of the three co-existing microphases: endcaps, cylinders and branching points. The right shift is linked to a continuous transformation of giant micelles into microemulsions containing an internal fluid. On the other hand, viscosity at maximum scales with the generalized bending constant of the molecular film forming the three microphases of the surfactant system. The total of four proposed mechanisms of solute-surfactant interactions that can impact amplitude and position of salt curves are independent and of different origin, but they are all intimately linked to the location of the additives within the surfactant film: headgroup, micellar interface, surfactant tail region or micellar core. Further investigation will be necessary to understand the molecular driving forces that position nonpolar additives within micellar aggregates, which would be the key for successful prediction of their impact on macroscopic viscosity.

International audience; We propose the statistical thermodynamic model for the prediction of the liquid–liquid extraction efficiency in the case of rare-earth metal cations using the common bis(2-ethyl-hexyl)phosphoric acid (HDEHP) extractant. In this soft matter-based approach, the solutes are modeled as colloids. The leading terms in free-energy representation account for: the complexation, the formation of a highly curved extractant film, lateral interactions between the different extractant head groups in the film, configurational entropy of ions and water molecules, the dimerization, and the acidity of the HDEHP extractant. We provided a full framework for the multicomponent study of extraction systems. By taking into account these different contributions, we are able to establish the relation between the extraction and general complexation at any pH in the system. This further allowed us to rationalize the well-defined optimum in the extraction engineering design. Calculations show that there are multiple extraction regimes even in the case of lanthanide/acid system only. Each of these regimes is controlled by the formation of different species in the solvent phase, ranging from multiple metal cation-filled aggregates (at the low acid concentrations in the aqueous phase), to the pure acid-filled aggregates (at the high acid concentrations in the aqueous phase). These results are contrary to a long-standing opinion that liquid–liquid extraction can be modeled with only a few species. Therefore, a traditional multiple equilibria approach is abandoned in favor of polydisperse spherical aggregate formations, which are in dynamic equilibrium.

Hypothesis The formation of transient networks of giant micelles leads to a viscosity peak when salt is added to aqueous solutions of charged surfactants. It is the consequence of an increase of the packing parameter due to charge screening of the surfactant headgroups, leading to a continuous transformation of the aggregates from spherical to wormlike micelles, and finally to branched networks. It should therefore be possible to predict the macroscopic viscosity of entangled giant micelles by modelling the packing parameter at nanoscale. Experiments A thermodynamic model is presented with a minimum of adjustable parameters, where branched networks are considered to be built from three coexisting microphases: cylinders, endcaps, and junctions. We use spontaneous packing parameters, in which the whole molecular length instead of the commonly used hydrocarbon chain length is considered. Standard reference chemical potentials and subsequently the occurrence of each microphase can be explicitly derived at specific electrolyte concentrations. Effective micellar length of giant micelles can be obtained from the microphase composition and is subsequently used to calculate the viscosity. Findings The model successfully predicts position and intensity of the viscosity maximum observed in experimental salt curves of sodium laureth sulfate (SLES). The robustness of the model was further investigated for various types of added salts or fragrance oils that affect differently spontaneous packing parameters or interfacial bending energy. An excellent agreement of the simulated salt curves with experimental data was achieved.

Mixtures of three solvents, with two immiscible liquids and a third one miscible to both - the solvotrope, may exhibit structuration. We explore the phase diagram of n-octanol/ethanol/water, where ethanol is the hydrotrope, varying composition from the water-rich side to the n-octanol-rich side at constant ethanol fraction. We resolve nanometer-sized structures experimentally by mean of four contrasts: three from Small Angle Neutron Scattering (SANS) and one from Small Angle X-ray Scattering (SAXS). On the water-rich side, we confirm the existence of droplets associated to a critical point stabilized by an excess adsorption of the hydrotrope: the ultra-flexible microemulsion (UFME) domain. The n-octanol-rich side is better described as a dynamic random network of chain-like associations of hydroxy groups. The continuous evolution from oil clusters to a dynamic network of hydroxy groups is demonstrated by the features of scattering patterns, successfully compared for all contrasts to Molecular Dynamics (MD) simulations, allowing to illustrate with snapshots the structuration of solvents. The free energy of transfer of the hydrotrope obtained from MD is low (∼1 k

Selectively exchanging metal complexes between emulsified water-poor microemulsions and concentrated solutions of mixed electrolytes is the core technology for strategic metal recycling. Nanostructuration triggered by solutes present in the organic phase is understood, but little is known about fluctuations of the microemulsion-water interface. We use here a modified version of an optoelectric device initially designed for air bubbles, in order to evidence resonant electrically induced surface waves of an oily droplet suspended in an aqueous phase. Resonant waves of nanometer amplitude of a millimeter-sized microemulsion droplet containing a common ion-specific extractant diluted by dodecane and suspended in a solution of rare earth nitrate are evidenced for the first time with low excitation fields (5 V/cm). From variation of the surface wave spectrum with rare earth concentration, we evidence uptake of rare-earth ions at the interface and at higher concentration the formation of a thin "crust" of liquid crystal forming at unusually low concentration, indicative of a surface induced phase transition. The effect of the liquid crystal structure on the resonance spectrum is backed up by a model, which is used to estimate crust thickness.

The theoretical description of systems with soft interfaces requires a precise definition of the interfaces that are present. Such definitions are common for interfaces of simple liquids and for surfactant assemblies like micelles, membranes, and microemulsions. Here, we focus on several possible rigorous definitions in a recently described surfactant-free microemulsion that consists of octanol, ethanol, and water, in which micelle-like aggregates are in dynamic equilibrium with the surrounding pseudo phase. We test different definitions that are based on the radial distribution functions of the components with respect to the center of these surfactant-free micelles. All definitions result in experimentally indistinguishable locations of the interface within the limits of resolution of light, X-ray, and neutron scattering experiments, since their locations differ by at most 0.4 nm, which corresponds to roughly 2-3 bond lengths.

We study the addition of electrolytes to surfactant-free microemulsions in the domain where polydisperse pre-Ouzo aggregates are present. As in previous studies, the microemulsion is the ternary system water/ethanol/1-octanol, where ethanol acts as co-solvent. Addition of electrolytes modifies the static X-ray and neutron scattering, and dynamic light scattering patterns, as well as the position of the miscibility gap, where spontaneous emulsification occurs upon dilution with water. All observations can be rationalized considering that electrolytes are either “salting out” the ethanol, which is the main component of the interface stabilizing the aggregates, or producing charge separation via the antagonistic ion effect discovered by Onuki et al. Amphiphilic electrolytes, such as sodium dodecylsulfate or sodium dietheylhexylphosphate, induce a gradual transition towards monodisperse ionic micelles with their characteristic broad scattering “peak”. In these micelles the ethanol plays then the role of a cosurfactant. Dynamic light scattering can only be understood by combination of fluctuations of aggregate concentration due to the vicinity of a critical point and in-out fluctuations of ethanol., Open Access Komponente aus der Allianzlizenz

In this review, we discuss the conditions for forming microemulsions, systems which are thermodynamically stable mixtures of oil and water made stable by the presence of an interfacial film containing surface active molecules. There are several types of microemulsions, depending largely on the stiffness of the amphiphilic monolayer that separates the oily and the aqueous micro-domain. We first discuss and compare the phase behaviour of these different types, starting from the classical microemulsion made from a flexible surfactant film but then also moving on to less classical situations: this occurs when the interfacial film is stiff or when microemulsions are formed in the absence of a classical surfactant. In the second part, we relate these different microemulsion types to the structural features as can be determined via different methodologies by small angle scattering (SAS). Using absolute scaling, general theorems as well as fitting under constraints or to pre-supposed shapes in real space or correlation functions in reciprocal space allows to classify all microemulsions into classical flexible, rigid or ultra-flexible microemulsions with either globular, connected cylinder of locally flat interfaces, with the corresponding conductivity and phase stability properties.

Bligh and Dyer (B & D) or Folch procedures for the extraction and separation of lipids from microorganisms and biological tissues using chloroform/methanol/water have been used tens of thousands of times and are “gold standards” for the analysis of extracted lipids. Based on the Conductor-like Screening MOdel for realistic Solvatation (COSMO-RS), we select ethanol and ethyl acetate as being potentially suitable for the substitution of methanol and chloroform. We confirm this by performing solid–liquid extraction of yeast (Yarrowia lipolytica IFP29) and subsequent liquid–liquid partition—the two steps of routine extraction. For this purpose, we consider similar points in the ternary phase diagrams of water/methanol/chloroform and water/ethanol/ethyl acetate, both in the monophasic mixtures and in the liquid–liquid miscibility gap. Based on high performance thin-layer chromatography (HPTLC) to obtain the distribution of lipids classes, and gas chromatography coupled with a flame ionisation detector (GC/FID) to obtain fatty acid profiles, this greener solvents pair is found to be almost as effective as the classic methanol–chloroform couple in terms of efficiency and selectivity of lipids and non-lipid material. Moreover, using these bio-sourced solvents as an alternative system is shown to be as effective as the classical system in terms of the yield of lipids extracted from microorganism tissues, independently of their apparent hydrophilicity.

Curious effects ranging from enzyme activity to anomalies in evapn. rates that have been known for over fifty years suggest the existence and thermodn. stability of surfactant-free micelles. Only recently, joint X-ray, light and neutron scattering expts. have demonstrated that aggregates and bulk pseudo-phases coexist in presumably normal solns., in which a water insol. component is solubilized in a certain domain of concn. of a hydrotrope component like ethanol. Nevertheless, nothing is known about the mol.-level shape and structure of such aggregates. In this work we characterize mixts. of octanol, ethanol, and water by mol. dynamics simulations. For compns. in the "pre-ouzo" region (close to the single phase stability limit) we observe micelle-like aggregates that are clearly distinct from simple crit. d. fluctuations. We define an ethanol partition in the pseudo-phase from an integral of the van der Waals dispersion energy term. From this partition, octanol-rich aggregates swollen with ethanol appear with an emerging interface. Ethanol is present in the water pseudo-phase with an exponential decay similar to the one predicted by Marcelja and Radic forty years ago., Open-Access-Komponente aus der Allinanzlizenz

Bligh and Dyer (B & D) or Folch procedures for the extraction and separation of lipids from microorganisms and biological tissues using chloroform/methanol/water have been used tens of thousands of times and are “gold standards” for the analysis of extracted lipids. Based on the Conductor-like Screening MOdel for realistic Solvatation (COSMO-RS), we select ethanol and ethyl acetate as being potentially suitable for the substitution of methanol and chloroform. We confirm this by performing solid–liquid extraction of yeast (Yarrowia lipolytica IFP29) and subsequent liquid–liquid partition—the two steps of routine extraction. For this purpose, we consider similar points in the ternary phase diagrams of water/methanol/chloroform and water/ethanol/ethyl acetate, both in the monophasic mixtures and in the liquid–liquid miscibility gap. Based on high performance thin-layer chromatography (HPTLC) to obtain the distribution of lipids classes, and gas chromatography coupled with a flame ionisation detector (GC/FID) to obtain fatty acid profiles, this greener solvents pair is found to be almost as effective as the classic methanol–chloroform couple in terms of efficiency and selectivity of lipids and non-lipid material. Moreover, using these bio-sourced solvents as an alternative system is shown to be as effective as the classical system in terms of the yield of lipids extracted from microorganism tissues, independently of their apparent hydrophilicity.

International audience; Herein, a minimal model for the common case of W/O solubilization of badly soluble compounds present in an excess phase by reverse micellar aggregates in chemical equilibrium with its single compounds is introduced. A simple model of such liquid-liquid extractions is crucial for obtaining predictive parameter for the modelling of nuclear waste management and hydrometallurgic recycling strategies. The standard Gibbs free energy of aggregation and the concentration of the corresponding aggregate is calculated within a multiple-equilibria approach for a set of aggregate compositions of solute and amphiphilic extractant molecules. This minimal model provides potential surfaces estimating the stability of different aggregate compositions with 6.2 kJ mol−1 as a generalized bending constant. The complete concentrations of free and aggregated extractant species as well as the favored aggregation numbers, the polydispersity, the activity of the organic solvent, and the critical concentrations are captured by this thermodynamic model. An increase of the apparent critical micelle concentration for an increasing solute content in the aqueous phase is detected by this method.

International audience; Ternary solutions containing one hydrotrope (such as ethanol) and two immiscible fluids, both being soluble in the hydrotrope at any proportion, show unexpected solubilization power and allow strange but yet unexplained membrane enzyme activity.We study the system-water-octanol as a simple model of such kinds of ternary solutions. The stability of “detergentless”micelles or microemulsions in such mixtures was proposed in the pioneering works of Barden and coworkers [Smith GD, Donelan CE, Barden RE (1977) J Colloid Interface Sci 60(3):488–496 and Keiser BA, Varie D, Barden RE, Holt SL (1979) J Phys Chem 83(10):1276–1281] in the 1970s and then, neglected, because no general explanation for the observations was available. Recent direct microstructural evidence by light, X-ray, and neutron scattering using contrast variation reopened the debate. We proposehere a general principle for solubilization without conventional surfactants: balance between hydration force and entropy. This balance explains the stability of microemulsions in homogeneous ternary mixtures based on cosolvents.

The effect of adding salts to micelles made of a sugar based surfactant, n-octyl-beta-glucoside, has been investigated using small angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. It was shown that adding salts leads to change the outer shell hydration of the micelles i.e. where the glucose moieties are situated. No ion adsorption at the micelle surface was detected. Three regimes have been determined as a function of the ionic strength (IS): (i) at low IS (

a b s t r a c t There is a still growing interest in the recovery of rare earth elements due to their manifold industrial and technological applications. We present here a simple and effective method for the enrichment of micrometer sized La2O3 particles via microparticle stabilized foams. By using the short chain amphiphile (1-hexyl)trimethylammonium bromide (C6TAB) foam that is generated by surface modified particles only can be generated. This technique allows a more selective and specific particle transport mechanism. The results are discussed in terms of surface charges and transport mechanisms. Furthermore, the effects of particle concentration, pH and amphiphile concentration are studied and evaluated. © 2012 Elsevier B.V. All rights reserved.

Due to their amphiphilic properties, malonamide molecules in alkane are organized in reverse micelle type aggregates, composed of a polar core formed by the malonamide polar heads and the extracted solutes, and surrounded by a hydrophobic shell made up of the extractant alkyl chains. The aggregates interact with one another through an attractive potential, leading to the formation of a third phase. This occurs with the splitting of the organic phase into a light phase composed mostly of diluent, and a heavy third phase containing highly concentrated extractant and solutes. In this article, we show that the aggregation (monomer concentration, domain of stability, and attractive potential between micelles) greatly depends on the nature of the extracted solute, whereas the size of aggregate (aggregation number) is only slightly influenced by this. We describe the extraction of water, nitric acid, neodymium nitrate and uranyl nitrate. Strongly polarizable species induce consistently large attraction potentials and a small stability domain for the dispersion of nanodroplets in the solvent. Highly polarizable ions such as lanthanides or uranyl induce more long-range attractive interactions than do protons.

Single particle light scattering (SPLS) has been extended towards sizes near 100 nm to measure particle size distributions with high precision and model free and thus to establish a diagnostic about the stage of aging emulsion properties. SPLS measurements on emulsions stabilized with catanionic crystals allowed to follow the evolution of droplet size distribution as a function of surface charge upon aging in the absence of Oswald ripening. Small angle neutron scattering (SANS) experiments allowed identification of the crystalline nature of the solids stabilizing these Pickering emulsions. The remarkably stable Pickering emulsions stabilized via catanionic microcrystals were in addition characterized by confocal microscopy and by ζ-potential measurements.

Three length scales have to be considered to describe microemulsions: persistence length, spontaneous radius of curvature of the surfactant film as intensive variables and finally the characteristic size imposed by the ratio of volume fraction to available specific area surface. The specific area per unit volume is an intensive variable linked to sizes and topologies that can be built without tearing the surfactant film. We show here that at least four types of bicontinuous microstructures have been detected so far, and that they can be distinguished by a simple experimental determination of the evolution of scattering peak position versus dilution. Besides the classical microstructures dominated by entropy or a priori considered as droplets, the other microstructures identified so far can be approximated as connected cylinders or randomly connected swollen bilayers. All these microstructures can be considered as “molten” precursors of the lyotropic liquid crystalline phases that are adjacent to microemulsions in phase diagrams.

We show that solubilization in microemulsion droplets is best described as a combination of interfacial adsorption and internal absorption. We progressively add solute to a Winsor type I system, and simultaneously measure the amount of solute at the oil–water interface and its effect on the interfacial curvature. We determine the relationship between the effective packing parameter and the amount of solute adsorbed at the oil–water interface. For four solutes, a significant amount of oil is co-extracted with solute into the interfacial film. Moreover, we show that solubilization in microemulsions can be characterized by two physical quantities with precise meaning: (1) the increase in interfacial area per molecule of adsorbed solute and (2) the number of oil molecules co-extracted with each solute molecule into the interfacial film. To quantify these effects, we introduce the constant interfacial thickness (CIT) model. It provides a general relationship between curvature, packing and interfacial composition in oil/water/surfactant/solute mixtures. Finally, we show that these results can be used to calculate the free energy of transfer of solute and oil from the droplet core to the interface.

The phase diagrams of ternary mixtures of partly miscible solvents containing a hydrotropic co-solvent exhibit a variable miscibility gap and one critical point. This work investigates the entire monophasic region far from and near to the miscibility gap in octan-1-ol/ethanol/water, for which ultra-flexible micro­emulsions (UFMEs) are observed by small-angle scattering techniques. SWAXS (combined small- and wide-angle X-ray scattering) allows the elucidation of these types of structure. Three distinct areas can be identified in the phase diagram, with scattering data resembling those from direct, bicontinuous and reverse local structures. These UFMEs are far more polydisperse than their surfactant-based counterparts. Water-rich and solvent-rich domains are only delimited by a small excess of hydrotrope, instead of a well defined surfactant layer of fixed area per molecule. It is shown that all scattering spectra obtained for the nanostructured compositions can be modelled by a simple unified analytical model composed of two uncorrelated contributions. The main one is the Ornstein-Zernike formula for composition fluctuations which gives information about the pseudo-phase domain size. The second is a Lorentzian that captures the structure of at least one of the coexisting pseudo-phases. No Porod law can be measured in the SAXS domain. The proposed expression gives access to two characteristic sizes as well as one inter-aggregate distance.The phase diagrams of ternary mixtures of partly miscible solvents containing a hydrotropic co-solvent exhibit a variable miscibility gap and one critical point. This work investigates the entire monophasic region far from and near to the miscibility gap in octan-1-ol/ethanol/water, for which ultra-flexible micro­emulsions (UFMEs) are observed by small-angle scattering techniques. SWAXS (combined small- and wide-angle X-ray scattering) allows the elucidation of these types of structure. Three distinct areas can be identified in the phase diagram, with scattering data resembling those from direct, bicontinuous and reverse local structures. These UFMEs are far more polydisperse than their surfactant-based counterparts. Water-rich and solvent-rich domains are only delimited by a small excess of hydrotrope, instead of a well defined surfactant layer of fixed area per molecule. It is shown that all scattering spectra obtained for the nanostructured compositions can be modelled by a simple unified analytical model composed of two uncorrelated contributions. The main one is the Ornstein-Zernike formula for composition fluctuations which gives information about the pseudo-phase domain size. The second is a Lorentzian that captures the structure of at least one of the coexisting pseudo-phases. No Porod law can be measured in the SAXS domain. The proposed expression gives access to two characteristic sizes as well as one inter-aggregate distance.

We show that three different morphologies exist near the two-phase boundary of ternary systems containing a hydrotropic cosolvent. Based on synchrotron small- and wide-angle X-ray scattering combined with molecular dynamics, we rationalize the specific scattering signature of direct, bicontinuous, and reverse mesoscale solubilization. Surprisingly, these mesostructures are resilient toward strong acids, which are required in industrial applications. However, on a macroscopic scale, the phase boundary shifts in salting-in and salting-out in the direct and respectively reverse regime, leading to a crossing of the binodals., Ultraflexible microemulsions that contain a hydrotropic cosolvent exist in three morphologies. Stability is reinforced by concentrated sulfuric acid in the water-rich corner and weakened in the octanol-rich corner.