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Even in the absence of surfactants, polymers, or particles, spontaneous emulsions produced by dilution with water can be stable over days. This “Ouzo effect” used by the industry is obtained by rapid dilution from an identified “pre-Ouzo” domain of composition where weak aggregates are present: nanometer-sized clusters covered by a surface layer enriched in a hydrotrope such as ethanol. In these systems, Ostwald ripening is not an effective destabilizing mechanism. Using in situ autodilution small-angle X-ray scattering (SAXS), we follow the morphological transitions occurring in a ternary mixture of water/n-octanol/ethanol throughout the monophasic and biphasic regions. This allows for the first time an online characterization of the multiscale coexisting microstructures. Small-angle neutron scattering (SANS) profiles on metastable emulsions as well as phase-separated samples complete the SAXS data, taking advantage of contrast variation via isotopic substitution. After crossing the phase boundary into the two-phase region, coexisting phases are both ternary solutions structured at the nanometer scale when the emulsion is stable. The transition from single phase to two phases is asymmetric around the plait point. When the initial concentration of the hydrotrope is below the minimum hydrotrope concentration (MHC), emulsification failure occurs, i.e., emulsions cream within seconds. Beyond MHC, the low interfacial tension between coexisting ternary fluids results in a Laplace pressure below 100 Pa, explaining the puzzling resilience of spontaneous emulsion to the universal mechanism of Ostwald ripening.

International audience; Porous media in extraction and especially pertraction are often suspected to add unnecessary diffusive resistance and considerably slow down extraction kinetics. In the practical case of the separation of rare earth compounds from water into an organic phase, the use of specific ion binding ligands in high concentrations is required. These tend to form complex liquid crystalline phases preferentially at ion-rich locations inside a pertraction membrane. We will report on the modeling of the behavior of such fluids in the case of pertraction as well as in the case of a miniaturized pertraction device. We will show that diffusive and reactive solute transport can be accurately simulated without any free parameters. 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.

International audience

International audience

International audience; We generate all possible thermalized microstructures of two non miscible liquids separated by a known amount of w/o interface and locate their domains of stability in ternary phase diagrams. Frus- trated and unfrustrated bicontinuous microemulsions appear near instabilities related to transition towards lyotropic liquid crystals. Microstructures can be distinguish via qualitative features on the scattering.

This work is a review of the effect of different monovalent anions (belonging to the Hofmeister series) on a single model amphiphile, phosphatidylcholine molecules in contact with water, in three different geometries, Langmuir monolayers, bilayers and micelles, which differ by area per molecule and radius of curvature. The zwitterionic lipids DPPC (1,2-dipalmitoyl-phosphatidylcholine) and DPC (Dodecylphosphocholine) have been used to form the three geometries. The salt solutions used were NaCl, NaBr, NaNO3, NaI, NaBF4, NaClO4 and NaSCN. Various interfacial and bulk experimental techniques were used in order to study the effect of the anions on the amphiphiles in the three geometries. The interfacial techniques used were surface pressure-area isotherms, Brewster angle microscopy (BAM), Grazing incidence X-ray diffraction (GIXD), infrared reflection absorption spectroscopy (IRRAS). The bulk sensitive techniques used were small-angle X-ray scattering (SAXS), osmotic stress (OS) and light scattering. The experimental results obtained from the three model systems indicate that the interfaces become charged through lipid-ion association. The results were fitted with appropriate theoretical models to provide "binding" or "partitioning" constants of anions in the headgroup region of the lipid molecules. The theoretical analysis strongly suggests that the anions do not associate with the lipid molecules through a local chemical reaction, but rather they partition inside the disordered lipid interfaces. © 2007 Elsevier B.V. All rights reserved. 303 1-2 144 158 Cited By :36

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