Liquid Interface Functionalized by an Ion Extractant: The Case of Winsor III Microemulsions

Caroline Bauer 1 Pierre Bauduin 1 Olivier Diat 1 Thomas Zemb 2
1 L2IA - Ions aux Interfaces Actives
ICSM - UMR 5257 - Institut de Chimie Séparative de Marcoule
2 LTSM - Tri ionique par les Systèmes Moléculaires auto-assemblés
ICSM - UMR 5257 - Institut de Chimie Séparative de Marcoule
Abstract : The present work shows for the first time that tributylphosphate (TBP), the major ion extractant used in the reprocessing of spent nuclear fuel, acts efficiently as a cosurfactant in the formation of three-phase microemulsions. The system is composed of water, dodecane, TBP, and an extremely hydrophilic sugar surfactant, n-octyl-β-glucoside. The investigation of the three-phase region (Winsor III), the so-called “fish-cut” diagrams, revealed that TBP exhibits cosurfactant behavior comparable to that of classical cosurfactants n-pentanol and n-hexanol. Upon increasing the cosurfactant/surfactant molar ratio, TBP appears to be more efficient than single-chain alcohols in raising the spontaneous curvature of the adsorbed surfactant film toward oil. This is a direct consequence of the different lateral packing of TBP and n-pentanol or n-hexanol in the mixed surfactant film, with TBP having three alkyl chains and so a higher hydrophobic volume than those n-alcohols. This property is underlined by the interfacial film composition, which is determined by the chemical analysis of the excess phases. It gives a surfactant to cosurfactant molar ratio of 1:1 for TBP and 1:3 for n-hexanol. Moreover, the local microstructure of the microemulsion becomes dependent on the addition of salt when n-alcohol is replaced by TBP. A specific salt effect is also observed and rationalized in terms of the complexing property of TBP and Hofmeister’s effects. Treatment of the small-angle neutron scattering (SANS) data gives access to (i) the length scales characterizing the microemulsions (i.e., the persistence length, ξ, and aqueous or organic domain sizes, D*) and (ii) the specific surface, Σ. It results that a subtle change is highlighted in the TBP microemulsion structure, in terms of connectivity, according to the type of salt added.
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https://hal.umontpellier.fr/hal-02106857
Contributeur : Olivier Diat <>
Soumis le : mardi 23 avril 2019 - 13:32:20
Dernière modification le : lundi 6 mai 2019 - 14:22:02

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Caroline Bauer, Pierre Bauduin, Olivier Diat, Thomas Zemb. Liquid Interface Functionalized by an Ion Extractant: The Case of Winsor III Microemulsions. Langmuir, American Chemical Society, 2011, 27 (5), pp.1653-1661. ⟨10.1021/la104005x⟩. ⟨hal-02106857⟩

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