Nanometric Surface Oscillation Spectroscopy of Water-Poor Microemulsions

Abstract

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.

Rapid Stabilization of Immiscible Fluids using Nanostructured Interfaces via Surfactant Association

“…However, research on dynamic phenomena in which structural self-assembly stabilizes the interface under nonequilibrium conditions is still in its infancy. This is despite the fact that in situ self-association of amphiphilic molecules has been widely observed for a variety of practical or industrial applications including oil recovery [45][46][47], flow instabilities [20,[48][49][50][51], biological systems [52][53][54], and rare metal extraction [55]. There has yet to be a fundamental study on dynamics of interfacial material formation between associating surfactants at immiscible liquid interfaces, and the connection between structure and property relationships, in addition to the underlying mechanism of structure development at the molecular level.…”

A microfluidic study of synergic liquid–liquid extraction of rare earth elements

“…Although, if in the classical extraction regime (Winsor II), we have shown in a previous paper that the chosen membrane is not a limiting factor, 33 it has recently been evidenced that liquid-liquid and liquid-solid interfaces increase the domain of stability of the liquid crystals that constitute the ''third phase''. 23 Therefore, the results concerning experiments where a third phase may be present in the pores of the membrane will have to be considered with care and with some uncertainty regarding the exact composition of the final equilibrium state.…”

“…Ion exchanges occur between aqueous (in blue) and solvent-rich phases (orange and light yellow). Kinetic barrier and asymmetry in the transfer rate are due to the thin interfacial domain, also called the interphase, 23 which is schematized as a green line. 97,98 Again, in the dilute phase, complexation versus entropy balance results in low but measurable energy of transfer.…”

“…In order to reduce time and volume, relying on microfluidic devices represents a very promising route. 15,[22][23][24][25][26][27][28][29][30][31] Indeed, since the pioneering work of Ismagilov and co-workers, 22 microfluidics has been developed as a popular method to save quantities of test materials needed to complete experimental plans in formulating efficient processes. The main difficulties in using microfluidics instead of the old ''batch'' method are related to the adsorption of electrolytes on all interfaces present and to the sensitivity required in elemental analysis.…”

Effects of porous media on extraction kinetics: Is the membrane really a limiting factor?

“…[29] The unusually high efficiency of TODGA is due to the formation of reverse micelles, as reviewed by Jensen et al [30] The interphase existing at the water/diluent interface has also been observed and studied in details recently by Nanometric Surface Oscillation Spectroscopy. [31] Varying the pH was also presenting a great interest beyond membrane characterization because obtaining efficiency in hydrometallurgy processes at high pH is the subject of intense research, as it enable to reduce process cost and the amount of effluent to be treated. [32] Validation of microfluidic membrane extraction results was performed by comparison to results obtained by batch extraction experiments.…”