Abstract
Liquid/liquid (L/L) interfaces play a key, yet poorly understood, role in a range of complex chemical phenomena where time-evolving interfacial structures and transient supramolecular assemblies act as gatekeepers to function. Here, we employ surface-specific vibrational sum frequency generation combined with neutron and X-ray scattering methods to track the transport of dioctyl phosphoric acid (DOP) and di-(2-ethylhexyl) phosphoric acid (DEHPA) ligands used in solvent extraction at buried oil/aqueous interfaces away from equilibrium. Our results show evidence for a dynamic interfacial restructuring at low ligand concentrations in contrast to expectation. These time-varying interfaces arise from the transport of sparingly soluble interfacial ligands into the neighboring aqueous phase. These results support a proposed "antagonistic" role of ligand complexation in the aqueous phase that could serve as a holdback mechanism in kinetic liquid extractions. These findings provide new insights into interfacially controlled chemical transport at L/L interfaces and how these interfaces vary chemically, structurally, and temporally in a concentration-dependent manner and present potential avenues to design selective kinetic separations.
| Original language | English |
|---|---|
| Pages (from-to) | 4886-4895 |
| Number of pages | 10 |
| Journal | Journal of Physical Chemistry B |
| Volume | 127 |
| Issue number | 21 |
| DOIs | |
| State | Published - Jun 1 2023 |
Funding
U.I.P., L.L., Y.-Z.M., N.A.T., and B.D. were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. V.B. and R.L.S. thank the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science & Engineering Division for partial financial support. Access to the Xeuss 3 SAXS/WAXS instrument was obtained via the ORNL instrumentation pool. The Xeuss 3 instrument was funded via the ORNL LDRD program. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operation by the Oak Ridge National Laboratory. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan )