A new type of fluorinated surfactant-free microemulsion: towards (fluorous-hydrogenous-aqueous) compartmentalized micelles

Abstract

Surfactant-free microemulsions (SFMEs) offer a promising alternative to classical microemulsions, avoiding the disadvantages associated to the use of conventional surfactants. A new type of SFMEs is reported in this work, in which aggregates with a fluorinated core enclosed in a hydrogenated corona, spontaneously form in an aqueous pseudo-phase. The liquid-liquid equilibrium (LLE) phase diagram of the ternary system (1H,1H-perfluoroheptanol + ethanol + water) was experimentally determined at 298.2 K. The single-phase region of the diagram was explored using a combination of experimental techniques and molecular dynamics (MD) simulations. Dynamic light scattering (DLS) measurements of solutions close to the plait point confirm the existence of micelle-like aggregates, rich in 1H,1H-perfluoroheptanol. Surface tension measurements of the same solutions exhibit a composition dependence that mimics that observed in surfactant-based systems. MD simulation results confirm the experimental results and provide a molecular level description of the organization. The novel SFME features an aqueous phase, formed by water and ethanol, coexisting with aggregates enriched in fluorinated alcohol, stabilized by ethanol molecules at their surface. Finally, gaseous xenon was dissolved in the SFMEs to probe their structure with 129Xe NMR spectroscopy. The NMR data confirm that xenon is preferentially dissolved within the fluorinated nonpolar domains of the SFMEs. Xenon medium shifts estimated from the MD simulations reproduce the experimental data with remarkable accuracy, validating the organization proposed by the simu lations and adding coherence to the whole methodology. These findings open new pathways for more sustainable SFMEs with fluorous domains as an alternative to the common fluorinated surfactant-based microemulsions, with potential for applications in the extraction of fluo rinated compounds from water.