Effect of alkyl chains configurations of tertiary amines on uranium extraction and phase stability - part II: Curvature free energy controlling the ion transfer

We consider a structural and thermodynamic analysis of uranium solvent extraction by tertiary amines for which the alkyl chain configuration has been modified. The first part of this work revealed that tertiary amines with longer or branched alkyl chains allow tuning the phase stability and uranium extraction by modifying the volume of the polar species extracted in the organic phase. A complete fit of SANS data confirms in this second part that this phenomenon is related to the supramolecular self-assembly of the tertiary amines into smaller reverse micelle like aggregates for longer or branched alkyl chains. It moreover shows that these smaller aggregates quench third phase formation thanks to reduced attractive interactions between them. A thermodynamic analysis based on the ienaic approach further rationalizes this effect by showing that alkyl chains have a significant effect on the aggregate's curvature free energy. The latter becomes a predominant inhibitor of uranium free energy of transfer due to the high entropic contribution originated by the extractants branching and packing. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study presents a structural and thermodynamic analysis of uranium solvent extraction using modified tertiary amines. The results indicate that tertiary amines with longer or branched alkyl chains can adjust phase stability and uranium extraction by modifying the volume of polar species in the organic phase. The experiments confirm that this phenomenon is related to the self-assembly of tertiary amines into smaller reverse micelle-like aggregates for longer or branched alkyl chains. The smaller aggregates also suppress third phase formation by reducing attractive interactions between them. A thermodynamic analysis reveals that alkyl chains significantly influence the aggregate's curvature free energy.