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A significant improvement in the sensitivity of a Huxley-Holmes design for a small angle X-ray scattering camera is obtained by separating the mirror and the monochromator. The "separated optics" camera described in this paper involves a long X-ray mirror close to a point X-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard X-rays allows precise calibration and hence absolute determination of sample cross-section by means of a semi-transparent beam-stop. In pinhole geometry, the flux corresponds to a ca. 107 photons/s through the sample, collimated to q=10-2 Å-1 in scattering vector range. This allows determination of scattered intensities of the order of 10-3 cm-1, corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. Values of absolute intensities for water as well as convenient widespread buffer solutions are shown, in order to be usable for calibration as secondary standards. As solid reference sample, the widely studied Lupolentm – a semi-crystalline polymer- is calibrated. The high-q limit (q ≃ 4.5 nm–1 ) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid-liquid dispersions.

A very small concentration of NaBr is added to ternary, transparent, and thermodynamically stable mixtures of water, ethanol, and octanol. Measuring the electrical conductivity along lines with constant water to ethanol ratios reveals remarkable composition dependencies similar to those found in classical surfactant-based microemulsions. Indeed, light-scattering experiments along the same composition lines and additional surface tension measurements confirm the onset of aggregation and possibly direct, bicontinuous, and reversed structures in these surfactant-free systems such as in classical microemulsions.

International audience; Quantitative experiments on the evaporation from sessile droplets of aqueous saline (NaCl) solutions show a strong dependence on salt concentration and droplet shape. The experiments were performed with seven decades of initial NaCl concentrations, with various droplet sizes and with different contact angles. The evaporaton rate is significantly lower for high salt concentrations and small contact angles than what is expected from the well-accepted diffusion-controlled evaporation scenario for sessile drops, even if the change of the vapor pressure due to the salt is taken into account. Particle tracking velocimetry reveals that this modification of the evaporation behavior is caused by Marangoni flows that are induced by surface tension gradients originating from the local evaporative peripheral salt enrichment. In addition it is found that already very low salt concentrations lead to a pinning of the three phase contact line. Whereas drops with concentration ≥ 10-6M NaCl are pinned as soon as evaporation starts, drops with lower salt concentration do evaporate in a constant contact angle mode. Aside from new, fundamental insights the findings are also relevant for a better understanding of the widespread phenomenon of corrosion initiated by sessile drops.

Recycling chemistry of metals and oxides relies on three steps: dissolution, separation and material reformation. We review in this work the colloidal approach of the transfer of ions between two complex fluids, i.e. the mechanism at the basis of the liquid-liquid extraction technology. This approach allows for rationalizing in a unified model transformation such as accidently splitting from two to three phases, or uncontrolled viscosity variations, as linked to the transformation in the phase diagram due to ion transfer. Moreover, differences in free energies associated to ion transfer between phases that are the origin of the selectivity need to be considered at the meso-scale beyond parameterization of an arbitrary number of competing “complexes”. Entropy and electrostatics are taken into account in relation to solvent formulation. By analogy with electronics dealing about electrons transported in conductors and semi-conductors, this “ienaic” approach deals with ions transported between nanostructures present in colloidal fluids under the influence of chemical potential gradients between nanostructures coexisting in colloidal fluids. We show in this review how this colloidal approach generalizes the multiple chemical equilibrium models used in supra-molecular chemistry. Statistical thermodynamics applied to self-assembled fluids requires only a few measurable parameters to predict liquid-liquid extraction isotherms and selectivity in multi-phase chemical systems containing at least one concentrated emulsified water in oil (w/o) or oil in water (o/w) microemulsion.

The coalescence behavior of two sessile drops that contain different chemical reactants (cerium nitrate and oxalic acid) and its impact on the formation of the solid precipitate (cerium oxalate) are investigated. With different liquids, the surface tension difference in the moment of drop-drop contact can induce a Marangoni flow. This flow can strongly influence the drop-drop coalescence behavior and thus, with reacting liquids, also the reaction and its products (through the liquid mixing). In our study we find three distinctly different coalescence behaviors ("barrier", "intermediate", "noncoalescence"), in contrast to only two behaviors that were observed in the case of nonreacting liquids. The amount of liquid mixing and thus the precipitation rate are very different for the three cases. The "intermediate" case, which exhibits the strongest mixing, has been studied in more detail. For high oxalic acid concentrations, mainly needle-like aggregates, and for low concentrations, mainly flower-like precipitate morphologies are obtained. In a transition range of the oxalic acid concentration, both morphologies can be produced. With the applied coalescence conditions, the different aggregate particles are arranged and fixed in a precipitate raft in a regular, periodic line pattern. This confirms the drop-drop coalescence configuration as a convection-reaction-diffusion system, which can have stationary as well as oscillatory behavior depending on the system parameters.

Some general principles of surfactant self-assembly are rationalised in order to give a short introduction to the use of phase diagrams for binary (two components) and ternary (three components) systems. Finally models for solubilisation are considered to be understood within the frame of those general packing principles: volume, surface and curvature conservation.

In this paper, we consider the effect of adding small carbohydrate solutes (small sugars) to DMPC (1,2-dimyristoyl- sn -glycero-3-phosphocholine) L α dispersions and the consequences on the force balance at zero osmotic pressure (maximal swelling). We show the importance of long incubations required to obtain samples at thermodynamic equilibrium where molecular diffusion has been completed. The monotonic increase of maximal swelling versus sugar content occurs as a combined effect of the screening of the van der Waals contribution and fluctuations in the lamellar stacks. According to this new approach, it is shown that changes in dielectric properties result in a much less pronounced effect than entropic forces (undulations) generated by the softening of the membranes at high sugar content. However, this sugar-induced swelling cannot be explained quantitatively by adding an entropic contribution to molecular interactions. Quantitative disagreement between the proposed mechanism and our observations is due either to nonadditivity of molecular interactions with entropic forces or to the relation used to account for the entropic contribution.

Our aim is to give a short introduction of the use of phase diagrams in order to rationalise general principles of surfactant self-assembly. These can be rationalised in terms of geometrical constraints: volume, surface and curvature. Binary (two components: surfactant and water) and ternary systems (surfactants, water, oil) are considered separately. Models for solubilisation, to be understood within the general principles and not as tabulated data, are presented. Finally, some examples of application of solubilisation in formulation are given. To cite this article: F. Testard, T. Zemb, C. R. Geoscience 334 (2002) 649–663.

Combining experiment with theory reveals the role of self-assembly and complexation in metal-ion transfer through the water-oil interface. The coordinating metal salt Eu(NO3)3 was extracted from water into oil by a lipophilic neutral amphiphile. Molecular dynamics simulations were coupled to experimental spectroscopic and X-ray scattering techniques to investigate how local coordination interactions between the metal ion and ligands in the organic phase combine with long-range interactions to produce spontaneous changes in the solvent microstructure. Extraction of the Eu(3+)-3(NO3(-)) ion pairs involves incorporation of the "hard" metal complex into the core of "soft" aggregates. This seeds the formation of reverse micelles that draw the water and "free" amphiphile into nanoscale hydrophilic domains. The reverse micelles interact through attractive van der Waals interactions and coalesce into rod-shaped polynuclear Eu(III) -containing aggregates with metal centers bridged by nitrate. These preorganized hydrophilic domains, containing high densities of O-donor ligands and anions, provide improved Eu(III) solvation environments that help drive interfacial transfer, as is reflected by the increasing Eu(III) partitioning ratios (oil/aqueous) despite the organic phase approaching saturation. For the first time, this multiscale approach links metal-ion coordination with nanoscale structure to reveal the free-energy balance that drives the phase transfer of neutral metal salts.

International audience; The thermodynamics and structural properties of flexible and rigid nonionic water/oil/surfactant microemulsions have been investigated using a two level-cut Gaussian random field method based on the Helfrich formalism. Ternary stability diagrams and scattering spectra have been calculated for different surfactant rigidities and spontaneous curvatures. A more important contribution of the Gaussian elastic constants compared to the bending one is observed on the ternary stability diagrams. Furthermore, influence of the spontaneous curvature of the surfactant points out a displacement of the instability domains which corresponds to the difference between the spontaneous and effective curvatures. We enlighten that a continuous transition from a connected water in oil droplets to a frustrated locally lamellar (oil in water in oil droplets) microstructure is found to occur when increasing the temperature for an oil-rich microemulsion. This continuous transition translated in a shift in the scattering functions, points out that the phase inversion phenomenon occurs by a coalescence of the water droplets.

The equation of state of a charged phospholipid (dioleoylphosphatidylserine: DOPS, Na+) in the absence of added salt is given at room temperature over six decades of osmotic pressure (100 to 2 × 108 Pa) covering the range of pressures where the different structures described previously have been observed.1 It is compared to the universal expression given by the Langmuir equation and predictions for the Gouy−Chapman regime for highly charged bilayers. Below membrane separations of 10 A, the pressure of solid supported DOPS films is higher than the prediction of the Langmuir equation. In the linear swelling regime of flat bilayers and up to the regime where giant correlated fluctuations are present (the oyster shell state), the Langmuir equation holds better than the prediction given by Attard et al.2 for the Gouy−Chapman regime. Close to maximum swelling (700 A), the pressure drops sharply. However, the universal power-law decay still holds in the unbinding regime, where the oyster shell state coexists wi...

We show the existence of a new and unexpected morphology of charged phospholipid membranes composed of pure dioleoylphosphatidylserine (DOPS, Na+) in the absence of added salt. This new morphology is characterized by giant collective fluctuations of locally lamellar stacks of membranes at the lamellar-to-vesicle unbinding transition. The DOPS dispersions have been studied in pure water and at rest using complementary techniques: small-angle scattering (neutron and X-ray) and freeze-fracture electron microscopy. In the present case of strong unscreened electrostatic interaction, we show that the order-to-disorder transition associated with the lamellar phase unbinding into vesicles is hidden by the presence of this intermediate state of strongly coupled undulating membranes where electrostatic and entropic forces compete. The giant collective fluctuations produce a texture analogous to that of an oyster shell as observed by freeze-fracture electron microscopy. Three microstructures are encountered along t...

The microstructure of a microemulsion is dominated by the thermodynamics of the surfactant interface between the oil and water domains. As the spontaneous curvature of this surfactant interface is strongly temperature dependent the microstructure of microemulsions also becomes temperature dependent. In the present work we have assumed that the thermodynamics of the interface is determined by the Helfrich Hamiltonian and that the interface can be described by two appropriately chosen level-cuts of a Gaussian random field. It is then possible to express the free energy density of the interface as a functional of the spectral distribution of the Gaussian random field so that the microstructure which minimizes the free energy can be determined by performing a functional minimization of the free energy with respect to the spectral distribution of the Gaussian random field. The two level-cuts are an important feature of the model since they allow us to model microemulsions with nonzero spontaneous curvature and...

6 I -(Cholest-5-en-3β-yloxycarbonyl)amino-6 I -deoxycyclomaltoheptaose and 6 I -(cholest-5-en-3α-ylamido)succinylamido-6 I -deoxycyclomaltoheptaose were synthesized and fully characterized by NMR spectroscopy experiments and mass spectrometry analysis. Incorporation of these monosubstituted amphiphilic cyclodextrins into phospholipid bilayers was investigated using small-angle X-ray scattering, differential scanning calorimetry and 31 P nuclear magnetic resonance. Different modes of incorporation depending on the spacer length between the cyclodextrin and cholesterol moieties were observed.

We show that organic rigid nanodisks of controlled size can be produced using a balanced pair of ionic surfactant molecules in a catanionic system. The counter-ion for the cationic surfactant is hydroxide. The counter-ion of the anionic surfactant is the hydronium ion. Close to equimolarity, counter-ions from water molecules: fluid solutions of ultra-low conductivity are obtained. This is solution contains rigid disks of thickness 4 nm: chains are frozen and surfaces are covered by ion pairs formed by the headgroups. The overall size of the disks is continuously adjustable from micrometer to nanometer size and is controlled by the excess of one of the two single chain surfactants involved. Unbound dispersed, nematic and lamellar structures are detected and located in the ternary equilibrium phase diagram at room temperature.

We establish experimentally the equation of state relating pressure and composition of a ternary model glycolipid/synthetic cationic surfactant/water system at room temperature. It is shown that an adhesion energy induced by the sugar headgroups is necessary to explain the presence of two distinct critical points that close two biphasic lamellar−lamellar zones. Between these two critical points, a turbid single-phase region is evidenced.

A gradient method to determine directly and quantitatively ternary phase diagrams is reported. The gradients are created in standard X-ray capillaries. 14C labeling and X-ray transmission measurements are used together in situ to obtain the exact sample composition along the gradient. Structural phase identification is obtained from SAXS analysis. Using this method, two cationic surfactant/glycolipid/water ternary systems have been investigated at different temperatures.

We show in the case of N,N'-dimethyl-N,N'-dioctyl-2-(2(hexyloxy)ethyl)-malonamide (DMDOHEMA) chosen as a typical oil-soluble extractant with surface activity that the free energy of formation of reverse micelles in the solvent phase strongly depends on the presence of polar solutes. Free energies per molecule vary typically from 0 to 2 kT per molecule (5 kJ mol(-1)), depending on the kosmotropic/chaotropic nature of the anion extracted. Variations of the reverse aggregation free energy introduced by acids and other co-extracted solutes as deduced from the critical aggregation concentrations cannot be neglected while modelling extraction. With typical aggregation numbers of 4-6, the free energy of formation of one reverse aggregate varies up to 20 kJ mol(-1), which is four times the typical difference in free energy of one single cation transfer between a "target" and a non-target ion in practical extraction and stripping industrial processes.

International audience; Fatty acids can self-assemble under various shapes in the presence of amines or cationic components. We assemble and compare these types of self-assembly leading toward a catanionic system either with a cationic surfactant or with an amine component playing the role of counter-ion. First, we focus on the molar ratio as a key driving parameter. Known and yet un-known values from other quantities governing the colloidal properties of these systems such as structural surface charge, osmotic pressure, molecular segregation, rigidity, in plane colloidal interactions and melting transition are discussed. We include also recent results obtained on the interfacial and foaming properties of these systems. We will highlight the specificity of these self-assemblies leading to unusual macroscopic properties rich of robust applications.

Non-electrostatic ion-specific effects are strong for anions when water is involved. We study here the thermodynamic equilibrium of a water-in-oil microemulsion stabilized by a surface-active extractant in a Winsor-II regime. Acid extraction isotherms for different anions located differently in the Hofmeister series have been investigated. A Langmuir like model was written for the specific case of acids treated as electrolytes, describing acid extraction as the adsorption of extracted electrolytes on the polar/apolar interface of the aggregates. Except for sulfate, isotherms can be described at first approximation as simple Langmuir-type isotherms when plotted as a function of the acid activity in the aqueous phase. The validity of the model being hence demonstrated, acid extraction free energies could be derived and compared, taking into account the effect of the anion position in the Hofmeister series. The case of phosphate, chloride, and sulfate as kosmotropes can be distinguished. They are significantly extracted, only above a threshold since the sphere-to-rod transition of the reverse aggregates has to be triggered by high chemical potential of the acid required to compensate anion dehydration.

In a solvent extraction process, the compositions of the phases in thermodynamic equilibrium (described as a Winsor-II regime) must be determined to obtain the extraction isotherms of ions as well as co-extracted water. By comparing the extractions of a series of acids by the malonamide DMDOHEMA (N,N’-dimethyl-N,N’-dioctyl hexylethoxy malonamide) in n-heptane, the specific anion effects regarding third phase formation and the strength of the acid - extractant interaction were investigated. It is shown that third phase formation is driven by hydration enthalpy of acid, while the polar core microstructure is controlled by the pKa of the acids. Upon acid extraction, the promotion of third phase formation follows the series H2SO4 ≈ H3PO4 ≈ HClO4 > HNO3 > HCl > HCOOH, which correlates to hydration enthalpy of acid in the case of monoacids. The combination of IR spectroscopy and DFT calculations revealed two different modes of acid extraction, either by hydrogen bonding (extraction of non-dissociated acid: HA) or by protonation of the extractant (extraction of dissociated acid: H+A−). The strength of the amide-acid interaction (protonation vs. hydrogen bonding) is correlated to the pKa of the acid and is responsible for the microstructure of the solution.

Des suspensions aqueuses de particules de bromopolystyrene ont ete caracterisees par diffusion de lumiere, diffusion de rayons X aux petits angles et par des mesures de pression osmotique. Nous avons ainsi etudie leur structure et les interactions interparticulaires en fonction de la fraction volumique a salinite constante de l'ordre de la micromole/1. Lorsque la cristallisation est lente, nous observons des cristaux parfaits cubiques centres par diffusion de lumiere pour des fractions volumiques comprises entre 0,04 et 0,7 % et cubiques faces centrees par diffusion de rayons X aux petits angles pour des fractions volumiques plus elevees (2-12 %). Apres cisaillement, des defauts apparaissent dans les cristaux ; ils sont caracterises par la disparition de certaines raies de Bragg en diffusion de lumiere pour des echantillons de fraction volumique comprise entre 0,1 et 0,3 % et par la presence d'un pre-pic observe par diffusion de rayons X aux petits angles avant le premier pic de Bragg, pour des echantillons plus concentres (2-12 %). Les pressions osmotiques ont ete mesurees par difference de pression hydrostatique entre la solution et le reservoir separes par une membrane hemipermeable. Les donnees experimentales sont bien reproduites par la theorie Poisson Boltzmann Reseau (PBR) qui montre que les interactions sont purement repulsives. Aucune force attractive faible de longue portee n'a ete detectee experimentalement. En calculant le deplacement moyen d'une particule a l'interieur de sa cage a l'aide du modele PBR excentre, nous avons verifie que le critere de Lindemann etait satisfait pour tous les cristaux observes. Cette etude a permis de determiner l'equation d'etat d'un cristal colloidal electrostatique. Les resultats sont equivalents a une mesure de force ultraprecise puisque les forces d'interaction mesurees entre particules sont de l'ordre de 10 -12 N pour des distances centre a centre de l'ordre de 4000 A.

The effect of a hydrophobically modified polysaccharide, cholesteryl-pullulan (CHP), on the swelling of the DMPC L α lamellar phase has been investigated by small angle neutron scattering. The CHP derivative can be introduced in the aqueous layers of the lamellar phase by anchoring lateral cholesterol groups into the bilayers. The resulting lamellar phase (L p ) is stabilized at large membrane separations by the introduction of a new repulsive and long range contribution in the force balance of the system. We emphasize here the temperature dependence of two coexisting lamellar phases (L α + L p ) differing in their polymer content and in their periodicities. At low polymer content (DMPC:CHP=99:1 by weight), the two lamellar phases at thermodynamic equilibrium change into a single phase on heating from room temperature to 50°C. The new phase (L p ′) is characterized by a very large correlation peak whose position is consistent with a lamellar structure following an ideal dilution law. The transition L α + L p → L p ′ is reversible on cooling, indicating that the observed coexistence of the two lamellar phases at room temperature is a true thermodynamic equilibrium. At higher polymer content (DMPC:CHP=95:5 by weight) the critical behaviour has not been observed. The periodicity of the L p phase slightly decreases on heating indicating a reduction in the miscibility gap and a possible critical point at temperatures higher than 50°C. However, in the investigated temperature range, the thermodynamic coexistence of the two lamellar phases is not affected in this case.

Partition coefficients of solutes between bilayers and water are determined with a new method, using contrast variation with SANS. The isotopic composition of the solvent that annuls the contrast is shown to depend on thermodynamical quantities related to the adsorption. Experimental results are given for two organic solute molecules (lactitol and aniline) in the favorable case of the swollen lamellar phase obtained with DDAB double chain surfactant.

We compare the influence of using either molecular or colloidal precursors on the synthesis of a ceramic material containing SiC and porous carbon. Remarkably, the temperature of synthesis for crystalline SiC is independent of the route chosen. The excess carbon in the initial mixture is the source of the excess porous carbon that binds to the crystalline domains of SiC in the final products. Interestingly, increasing the initial area of surface contact between carbon and silicon in the ceramic precursor results in different porosities in the ‘meso’ range. Simultaneous control of the size and the relative amounts of Si and C in the precursors allows control to be exerted over the nature and texture of the final powders. A simple and general mechanism is herein proposed to explain the evolution of the surface area as a function of the volume fraction of residual carbon in the synthesised ceramic.

Recently, it has been pointed out that the structure of shear ordered colloidal dispersions can adequately be accounted for by the intensity distribution I(l) along Bragg rods [Phys. Rev. Lett. 75, 763 (1995)]. Information concerning packing of the shear induced layers and on their stacking order is contained in I(l). In this paper I(l) is determined by measuring the small angle neutron scattering distribution as a function of the sample orientation. For the investigated charge stabilized system with particle diameter σ=143 nm and a distance of nearest neighbors in the layers a=237 nm, a structure close to random close‐packed hexagonal layers is found. As compared with close‐packed systems the distance between the layers c is elongated so that c≊a. Further, it is shown that the application of shear leads to a more uniform distribution of I(l) along the rods, which demonstrates that the loss of correlation between the hexagonal layers under sheared conditions can also be determined by small angle neutron scattering.

The effect of carbohydrates on the swelling of the DMPC Lα phase has been studied by small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS). The carbohydrates are glucose, ol...

International audience; Separation of metals in the cationic form is the basis of hydrometallurgy. Ion‐specific separation is achieved via selective transfer between liquid phases that have been emulsified in order to be in “close” contact. We show here how the organization of water‐in‐oil (w/o) “reverse” aggregates in the solvent phase controls the free energy of transfer of cations in the form of neutral salts between phases. Indeed, all known efficient ion separation mechanisms rely on complex fluids in the Winsor II regime, i.e. when a concentrated mixed salt solution is in equilibrium with a solvent phase containing self‐assembled aggregates. Here, we point out that, in the general case of water‐poor complex fluids containing extractant molecules, long‐range interactions linked to w/o interface curvature participate in the selectivity of any multivalent ion extraction process. The free energy related to ion transfer between phases, i.e. the extraction free energy, is different from the complexation free energy. This difference is the key to the selectivity of the separation process. We give here general expressions linking complexation free energy and transfer free energy as derived from known adsorption isotherms, taking into account interfacial curvature, considered as a generalized scalar related to the packing near the interface.

International audience; We report the specific effects of a series of anions (chloride, nitrate, and oxalate) on the solubility and self-assembly of cationic cetylpyridinium surfactants in water. The anion influence on micellization was evidenced by tensiometry and determination of Krafft temperatures. Anions strongly affect these parameters, depending on their position in the lyotropic series as well as on their “bridging” character. Scattering techniques (light, X-rays, and neutrons) were used to characterize the structures of micelles, and by solving a lateral equation of state approach, we show that chaotropic anions can be considered as adsorbed on the pyridinium head groups, inducing a decrease of the surface polarity and a Krafft temperature shift. Mixing different counteranions in various ratios led to a competition with a preferential adsorption at the micellar surface.

The effects of salt impregnation are studied within wood cell walls, occurring upon soaking from concentrated salt solutions. Osmotic deswelling is in some cases followed by ion specific swelling linked to Hofmeister effects. Taking into account microstructure, this study models the free energy changes associated with the ions and water uptake at molecular, colloidal, and macroscopic mechanical scales, to show that slow swelling until osmotic equilibrium originates from charge separation of the salt diffused into wood cell wall material. Kinetic effects as well as mechanical effects linked to transfer of species and swelling of the interstitial matrix between cellulose crystals are discussed. Predictions by minimal models taking into account nonelectrostatic ion complexation allow to estimate the order of magnitude of the nonelectrostatic binding free energy of adsorbed chaotropic anions and complexed divalent cations to be 8 and 10 kJ mole–1, respectively.

In liquid-liquid extraction, synergism emerges when for a defined formulation of the solvent phase, there is an increase of distribution coefficients for some cations in a mixture. To characterize the synergistic mechanisms, we determine the free energy of mixed coassembly in aggregates. Aggregation in any point of a phase diagram can be followed not only structurally by SANS, SAXS, and SLS, but also thermodynamically by determining the concentration of monomers coexisting with reverse aggregates. Using the industrially used couple HDEHP/TOPO forming mixed reverse aggregates, and the representative couple U/Fe, we show that there is no peculiarity in the aggregates microstructure at the maximum of synergism. Nevertheless, the free energy of aggregation necessary to form mixed aggregates containing extracted ions in their polar core is comparable to the transfer free energy difference between target and nontarget ions, as deduced from the synergistic selectivity peak.

The physicochemical behavior of crystalline silicon under acoustic cavitation is investigated in water sparged with argon at low temperature (10 and 20 °C). Surprisingly, spectroscopic investigations reveal that argon (bubbling continuously through the liquid phase during experiments) can be ultrasonically excited via mechanoluminescence, i.e., emission of light caused by mechanical action on a solid. This phenomenon is highlighted for the first time on an extended solid surface using these conditions and results from an interaction between the acoustically generated bubbles and the Si surface. The concomitant physical and chemical transformations induced at the solid–liquid interface are investigated (SEM, AFM) to characterize the generated stress and defects in combination with the roughness and wettability increases (evolving from ∼46° to ∼4°). Phase transformations of the Si lattice are observed (Raman spectroscopy, TEM) evidencing the complex stress state induced by acoustic cavitation in the Si crys...

On tie-lines between water-rich and alkane-rich solutions, it is shown via scattering experiments that natural lipopeptide surfactin self-assembles into direct and reverse micelles in equilibrium. Elongated direct micelles in the aqueous phase are present together with small reverse globular aggregates in the organic phase. These latter are made from hydrated surfactant without any "water pool" in the organic phase. The resulting biphasic system is used for liquid-liquid extraction of model metal cations. It is efficient with iron but not with copper or neodymium. Competitive extractions show high selectivity towards iron.

Self-assembly is ubiquitous in nature and in surfactant science.1 Globular micelles or vesicles in water are usually obtained with surfactants2 or amphiphilic block copolymers3 composed of a hydrophilic part and a hydrophobic part. The aggregation mechanism is then controlled by the tendency of the nonpolar part to avoid contact with water, known as the hydrophobic effect,4 while the polar part tends to be strongly hydrated. Consequently, the minimum free energy is reached during the aggregation process by minimal contact of the hydrocarbon chains with water and by maximal entropy that lead to the formation of the smallest possible aggregates, that is, spherical micelles for single-chain surfactants. As the concentration increases, the shape changes from spherical micelles to rods (hexagonal phase) to a lamellar phase, that is, from high to low curvature toward the apolar part.5 Double-chained surfactants, or some block copolymers with a pronounced hydrophobic tendency, cannot pack into spheres because of steric reasons, and are forced immediately into closed bilayers (vesicles) of near-zero curvature at the surfactant/copolymer scale.6 Recently, the formation of vesicles has been reported for more exotic, that is, non-amphiphilic chemical systems such as amino acid derivatives, oligopeptides, cyclodextrins, macrocycles, fluorofullerenes, and polyelectrolytes.7 Herein we show that the cobaltabisdicarbollide (mono-) anion (H+[3,3′-Co(1,2-C2B9H11)2]− (H+COSAN−; Figure 1) forms monolayer vesicles at low concentrations in water. An increase in concentration leads to a phase transition from vesicles to small micelles (Figure 1) and results in the coexistence of both aggregation states at higher concentrations. The formation of monolayer vesicles and small micelles was hitherto unknown for water-soluble carborane derivatives. peer-reviewed

International audience; An amphiphilic hexapeptide has been used as a model to quantify how specific ion effects induced by addition of four salts tune the hydrophilic/hydrophobic balance and induce temperature-dependant coacervate formation from aqueous solution. The hexapeptide chosen is present as a dimer with low transfer energy from water to octanol. Taking sodium chloride as the reference state in the Hofmeister scale, we identify water activity effects and therefore measure the free energy of transfer from water to octanol and separately the free energy associated to the adsorption of chaotropic ions or the desorption of kosmotropic ions for the same amphiphilic peptide. These effects have the same order of magnitude: therefore, both energies of solvation as well as transfer into octanol strongly depend on the nature of the electrolytes used to formulate any buffer. Model peptides could be used on separation processes based on criteria linked to “Hofmeister” but different from volume and valency.

International audience; The present work shows for the first time that tributylphosphate (TBP), the major ion extractant used in thereprocessing of spent nuclear fuel, acts efficiently as a cosurfactant in the formation of three-phase microemulsions.The system is composed of water, dodecane, TBP, and an extremely hydrophilic sugar surfactant, n-octyl-β-glucoside.The investigation of the three-phase region (Winsor III), the so-called “fish-cut” diagrams, revealed that TBP exhibitscosurfactant behavior comparable to that of classical cosurfactants n-pentanol and n-hexanol. Upon increasing thecosurfactant/surfactant molar ratio, TBP appears to be more efficient than single-chain alcohols in raising thespontaneous curvature of the adsorbed surfactant film toward oil. This is a direct consequence of the different lateralpacking of TBP and n-pentanol or n-hexanol in the mixed surfactant film, with TBP having three alkyl chains and so ahigher hydrophobic volume than those n-alcohols. This property is underlined by the interfacial film composition, whichis determined by the chemical analysis of the excess phases. It gives a surfactant to cosurfactant molar ratio of 1:1 forTBP and 1:3 for n-hexanol. Moreover, the local microstructure of the microemulsion becomes dependent on theaddition of salt when n-alcohol is replaced by TBP. A specific salt effect is also observed and rationalized in terms of thecomplexing property of TBP and Hofmeister’s effects. Treatment of the small-angle neutron scattering (SANS) datagives access to (i) the length scales characterizing the microemulsions (i.e., the persistence length, ξ, and aqueous ororganic domain sizes, D*) and (ii) the specific surface, Σ. It results that a subtle change is highlighted in the TBPmicroemulsion structure, in terms of connectivity, according to the type of salt added.

We demonstrate here that microemulsions with an IL as the continuous phase can be formed so that they are stable over a wide temperature range and have intermediary properties between flexible and stiff microemulsions. Three components (1-ethyl-3-methylimidazolium ethylsulfate ([emim][etSO(4)]), limonene, and octylphenol ethoxylate (Triton X 100, abbreviated as TX-100)) were used. This ternary system has been characterized from ambient temperature down to -10 °C by means of conductivity, viscosity, and small-angle X-ray scattering (SAXS) measurements. The SAXS data exhibit a characteristic single, broad scattering peak in conjunction with a typical q(-4) decay at large q values. The SAXS data have also been interpreted in terms of a dimensionless dilution plot, demonstrating that microstructures are neither isolated droplets nor a random flexible film structure but resemble molten liquid crystals (i.e., they are formed from locally cylindrical or planar structures). This semirigidity is attributed to a good match between the surfactant and the ionic liquid; this holds in a temperature range well below 0 °C.

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich., This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively., In this paper the mechanism behind the stabilization of Pickering emulsions by stacked catanionic micro-crystals is described. A temperature-quench of mixtures of oppositely charged surfactants (catanionics) and tetradecane from above the chain melting temperature to room temperature produces stable oil-in-water (o/w) Pickering emulsions in the absence of Ostwald ripening. The oil droplets are decorated by stacks of crystalline discs. The stacking of these discs is controlled by charge regulation as derived from conductivity, scattering and zeta potential measurements. Catanionic nanodiscs are ideal solid particles to stabilize Pickering emulsions since they present no density difference and a structural surface charge which is controlled by the molar ratio between anionic and cationic components. The contact angle of catanionic nanodiscs at a water/oil interface is also controlled by the non-stoichiometry of the components. The resulting energy of adhesion and the repulsion between droplets is much larger than kT. As a consequence of these unique properties of nanodiscs, this type of emulsions presents an extremely high resistance towards coalescence and creaming, even in the presence of salt.

Bicontinuous microemulsions are investigated as a model system for the specific adsorption phenomena of metal ions at the water-oil interface. Mixing an extremely hydrophobic ion extractant – tributyl phosphate (TBP) used here as co-surfactant – with an extremely hydrophilic sugar-based surfactant, we describe a new type of functionalized microemulsions that shows the classical Winsor phases, by varying the surfactant/extractant ratio. We focus on the Winsor III-type microemulsions by determining the phase diagrams whereas the microstructures were accessed by performing small angle neutron scattering experiments. Ultimately, these microemulsions may pave the way for the design of new selective ion extraction processes.

Power ultrasound (20 kHz, Iac = 20−56 W cm−2) was used to investigate physical and chemical effects of acoustic cavitation at the water−glass interface. Physical effects were characterized with different techniques of microscopy (optical, SEM, AFM) and were shown to increase and evolve as a function of sonication duration according to two distinctive periods: (i) an incubation period that initiates weak points on a glass surface, which may be the result of acoustically created shock-waves, and (ii) a second period of erosion, which is related to direct impact fracture erosion of the material. Chemical analysis of water (ICP-OES), after ultrasonic treatment, clearly indicates that bubble collapse at the water−glass interface initiates not only mechanical erosion but also accelerates the leaching processes of the glass components.

6 I -(Cholest-5-en-3β-yloxycarbonyl)amino-6 I -deoxycyclomaltoheptaose and 6 I -(cholest-5-en-3α-ylamido)succinylamido-6 I -deoxycyclomaltoheptaose were synthesized and fully characterized by NMR spectroscopy experiments and mass spectrometry analysis. Incorporation of these monosubstituted amphiphilic cyclodextrins into phospholipid bilayers was investigated using small-angle X-ray scattering, differential scanning calorimetry and 31 P nuclear magnetic resonance. Different modes of incorporation depending on the spacer length between the cyclodextrin and cholesterol moieties were observed.

International audience; Mixtures of ionic surfactants of opposite charge ("catanionic" mixtures) show strongly nonideal behaviors, for example, in terms of evolution of surface tension, critical micelle concentration, or morphology with respect to composition in each surfactant. In several catanionic systems, it has been proposed that the interaction between both surfactants is so strong that lateral phase segregation occurs within bilayers, with crystallites of preferential composition demixing from the excess of the other surfactant. Here, we investigate the temperature-composition phase diagram of the myristic acid/cetyltrimethylammonium mixtures. Combining microcalorimetry, X-ray diffusion, and solid-state deuterium NMR, we demonstrate that no separation is observed in the gel (L(beta)) state. The catanionic mixtures therefore behave like two-dimensional solid solutions with a negative azeotrope: the existence of a composition at which a maximum in melting temperature is observed does not imply the existence of a preferential crystal of this composition, but results from the preferential attraction between unlike amphiphilic molecules. Additionally, this study reveals the presence of a so-called intermediate phase, that is, a phase that shows dynamic properties intermediate between that of the L(beta) and the L(alpha) phases

Our understanding of the ``long range'' electrodynamic, electrostatic, and polar interactions that dominate the organization of small objects at separations beyond an interatomic bond length is reviewed. From this basic-forces perspective, a large number of systems are described from which one can learn about these organizing forces and how to modulate them. The many practical systems that harness these nanoscale forces are then surveyed. The survey reveals not only the promise of new devices and materials, but also the possibility of designing them more effectively.

Silicon carbide (SiC) and zirconium carbide (ZrC) powders were synthesized by the carbothermal reduction reaction of carbon and the corresponding metal oxide silica or zirconia respectively. The physical and chemical properties of the final products were studied according to the nature of precursors used: colloidal or micrometric powders for the oxides, sucrose, mannitol or sorbitol for the reducing agent. After mixing and freeze drying of these components, the powder was heated at temperatures ranging from 1300 and 1550°C under flowing argon to obtain the carbides. Depending on the nature of the precursors (colloidal or micrometric) an increase of more than one order in the magnitude of the surface area was observed. The highest surface area (300m2/g) was measured on a ZrC+C compound type elaborated from a colloidal precursor. The use of colloids in carbothermal reaction could be a route to control pore size in mesoporous carbides or supported porous carbon materials.