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Separation of rare earth compounds from water into an organic phase in practical cases requires the use of specific ion binding ligands in high concentrations. These tend to form complex liquid crystalline phases preferentially at ion-rich locations inside a pertraction membrane. They form a blocking layer above an ion concentration threshold, which is experimentally characterized. It is shown to limit the flux through the membrane, which is studied for the application of rare earth recycling, an example being the phase transfer of Nd from water into organic phase. This feedback leads to a stationary membrane permeation rate that can be modeled without any free parameters in very good agreement with experiment. The ion-specific formation and dissolution of the blocking layer, a feature found also in nature, and its control suggest further studies to enhance permeation as well as its selectivity control.

Calcium hydroxide forms unstable reactive nanoparticles that are stabilized when they are dispersed in ethylene glycol or 2-propanol. The aggregation behavior of these particles was investigated by contrast-variation small-angle neutron scattering (SANS), combined with small-angle X-ray scattering (SAXS). Nanoparticles on the order of 100 nm were found to aggregate into mass-fractal superstructures in 2-propanol, while forming more compact agglomerated aggregates with surface fractal behavior in ethylene glycol. Commensurate specific surface areas evaluated at the Porod limit were more than an order of magnitude greater in 2-propanol (approximately 200 m2.g(-1)) than in ethylene glycol (approximately 7 m2.g(-1)). This profound microstructural evolution, observed in similar solvents, is shown to arise from competitive solvent adsorption. The composition of the first solvent layer on the particles is determined over the full range of mixed solvent compositions and is shown to follow a quantifiable thermodynamic equilibrium, determined via contrast-variation SANS, that favors ethylene glycol over 2-propanol in the surface layer by about 1.4 kJ.mol(-1) with respect to the bulk solvent composition.

We show that it is possible to measure the porosity of facetted micron-sized hollow icosahedra of catanionic solutions by performing fluorescence recovery after photobleaching measurements. The size of spontaneous permanent pores in bilayers formed via molecular segregation is compatible with what is observed by freeze-fracture electron microscopy and is discussed versus theoretical expressions of bending energy.

The investigation of the dilute range in the system of myristic acid, cetyltrimethylammonium hydroxide, and water shows that the formation of charged catanionic microcrystallites induces measurable osmotic pressures. In the coexistence region between the lamellar phase and the disk phase, we observe a slight osmotic pressure drop, which is due to the crossing of tie lines during dilution. With the application of the Poisson−Boltzmann theory, the surface charge densities of icosahedral and disklike particles are estimated to determine the equation of state of these self-assembled aggregates in the dilute regime. In typical conditions, a hollow crystallite of 1-μm diameter has an effective charge on the order of 1.8 × 106, while the structural charge is 1 order of magnitude larger.

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...

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.