Title: Understanding Self-Assembly and the Stabilization of Liquid/Liquid Interfaces: The Importance of Ligand Tail Branching and Oil-Phase Solvation

Abstract

Organophosphorus-based ligands represent a versatile set of solvent extraction reagents whose chemical makeup plays an important role in extraction mechanism. We hypothesize that the branching of the extractant hydrophobic tail and its oil-phase solvation affect the liquid/liquid interfacial structure. Understanding the structure mediated adsorption and interfacial ordering becomes key in designing ligands with enhanced selectivity and efficiency for targeted extractions. We employed vibrational sum frequency generation spectroscopy and interfacial tension measurements to extract thermodynamic adsorption energies, map interfacial ordering, and rationalize disparate behaviors of model di-(2-ethylhexyl) phosphoric acid and dioctyl phosphoric acid ligands at the hexadecane water interface. With increased surface loading, ligands with branched hydrophobic tails formed stable interfaces at much lower concentrations than those observed for ligands with linear alkyl tails. The lack of an oil phase and associated solvation results in markedly different interfacial properties, and thus measurements made at air/liquid surfaces cannot be assumed to correlate with the processes occurring at buried liquid/liquid interfaces. Here, we attribute these differences in the surface mediated self-assembly to key variations in hydrophobic interactions and tail solvation taking place in the oil phase demonstrating that interactions in both the polar and nonpolar phases are essential to understand self-assembly and function.

Authors:

Doughty, Benjamin L.  ^[1];

• Search DOE PAGES for author "Doughty, Benjamin L."
• Search DOE PAGES for ORCID "0000-0001-6429-9329"

Premadasa, Uvinduni  ^[1];

• Search DOE PAGES for author "Premadasa, Uvinduni"
• Search DOE PAGES for ORCID "0000-0003-0289-2965"

Ma, Yingzhong  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-8154-1006"

Sacci, Robert  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-0073-5221"

Bocharova, Vera  ^[1];

• Search DOE PAGES for author "Bocharova, Vera"
• Search DOE PAGES for ORCID "0000-0003-4270-3866"

Thiele, Nikki  ^[1]

• Search DOE PAGES for author "Thiele, Nikki"
• Search DOE PAGES for ORCID "0000-0003-3301-0849"

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Thu Nov 18 00:00:00 EST 2021

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division

OSTI Identifier:

1837861

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Colloid and Interface Science

Additional Journal Information:

Journal Volume: 609; Journal Issue: 1; Journal ID: ISSN 0021-9797

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Nonlinear spectroscopy; Sum frequency generation; Solvent extraction; Liquid-liquid interface; Air-liquid interface; Molecular ordering; Oil phase interactions; Vibrational spectroscopy; Interfacial analysis; Interfacial tension