Tuneable interphase transitions in ionic liquid/carrier systems via voltage control

Area of Science:

• Electrochemistry
• Materials Science
• Surface Chemistry

Background:

• Ionic liquids (ILs) exhibit unique interfacial properties influenced by their structure and electric fields.
• Understanding the electric double-layer (EDL) structure is crucial for controlling IL behavior at interfaces.

Purpose of the Study:

• To investigate the electrical response and interfacial structure of non-halogenated phosphonium orthoborate ionic liquids.
• To elucidate the self-assembly mechanisms and voltage-dependent transitions of ILs at an electrified interface.

Main Methods:

• Quartz crystal microbalance (QCM) to measure electrical response under varying voltage.
• Neutron reflectivity (NR) to confirm interfacial structuring and compositional changes.
• Analysis of ion structure and solvent polarizability effects on IL behavior.

Main Results:

• One IL displayed anomalous electro-responsivity, indicating a cation self-assembly bilayer structure.
• This structure transitioned to a typical EDL at higher positive potentials.
• NR confirmed cation-dominated self-assembly at negative/neutral voltages, shifting to an anion-rich layer at positive potentials.

Conclusions:

• An interphase transition governs the electro-responsive behavior of self-assembling IL/carrier systems.
• Findings are pertinent for the application of ionic liquids in tribology and electrochemistry.
• The study highlights the importance of interfacial structuring in IL performance.