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Structure and anomalous underscreening in ethylammonium nitrate solutions confined between two mica surfaces
Y K Catherine Fung1, Susan Perkin1
1Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK. susan.perkin@chem.ox.ac.uk.
Faraday Discussions
|July 17, 2023
Summary
Anomalous underscreening, long-range interactions in ionic liquids, was studied in protic solvents. Ethylammonium nitrate (EAN) solutions showed similar underscreening effects, offering new insights into charge distribution in these electrolytes.
Area of Science:
- Physical Chemistry
- Materials Science
- Electrochemistry
Background:
- Long-range interactions in ionic liquids and concentrated electrolytes often exceed theoretical predictions (Debye-Hückel, liquid state theory), a phenomenon termed 'anomalous underscreening'.
- Previous experimental studies primarily focused on aprotic ionic liquids, leaving the behavior in protic ionic liquids less explored despite differing charge distributions.
Purpose of the Study:
- To investigate anomalous underscreening in protic ionic liquids, specifically ethylammonium nitrate (EAN) and its aqueous mixtures.
- To understand the influence of protic nature on charge interactions and near-surface phenomena.
Main Methods:
- Utilized a surface force balance to directly measure interaction forces between surfaces as a function of separation distance.
- Examined solutions of ethylammonium nitrate (EAN) across a range of volume fractions (10% to 100% EAN) mixed with water.
Main Results:
- Observed anomalous underscreening in protic ionic liquid (EAN) solutions, consistent with findings in aprotic ionic liquids.
- Revealed detailed information on near-surface ordering and dynamics at the EAN-mica interface.
Conclusions:
- Anomalous underscreening is not exclusive to aprotic ionic liquids and is also present in protic systems like EAN.
- The study provides crucial experimental data on interfacial behavior and charge interactions in protic ionic liquids, contributing to a broader understanding of electrolyte behavior.
