Spontaneous Ouzo Emulsions Coexist with Pre-Ouzo Ultraflexible Microemulsions

Sylvain Prévost*, Sebastian Krickl, Stjepan Marčelja, Werner Kunz, Thomas Zemb, Isabelle Grillo

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    23 Citations (Scopus)

    Abstract

    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.

    Original languageEnglish
    Pages (from-to)3817-3827
    Number of pages11
    JournalLangmuir
    Volume37
    Issue number13
    DOIs
    Publication statusPublished - 6 Apr 2021

    Fingerprint

    Dive into the research topics of 'Spontaneous Ouzo Emulsions Coexist with Pre-Ouzo Ultraflexible Microemulsions'. Together they form a unique fingerprint.

    Cite this